FinFish Biology and Feeding Habits

POWER RANGERNOTES BIOLOGY OF FINFISHES
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BIOLOGY OF FINFISH
1. Food and feeding habits
1.1.1 Food and feeding habits
Food and feeding habits of fishes is an interesting part of the biology to understand the type and nature of food they
consume and their place in the ecosystem as well. Feeding is essential for growth, maintenance and reproduction in fishes.
The fishes exhibit feeding habits from simple filter feeding to highly predatory life. The feedings habits of fishes are
assessed by:
1. Field observations
2. Analysis of gut contents
3. Laboratory experiments.
1.1.2 Categories of food
Food available in the nature can be classified as plankton, nekton, benthos and detritus.
Plankton : Plankton is microscopic organisms with little or no power of locomotion. They drift at the mercy of water
currents. They are broadly grouped into 2 categories depending on the presence or absence of plant pigments.
1. Phytoplankton – having chlorophyll in the cells e.g. Diatoms, Dinoflagellates
2. Zooplankton – without chlorophyll e.g. Copepods, crustacean larvae,other microscopic invertebrates
Nekton : Nekton are actively swimming organisms capable of independent movement. They actively maintain their
position despite the drifting water currents. They may be present at the surface (pelagic) or at the bottom (demersal) of
water column. e.g. fishes, shrimps, cuttlefishes and squids.
Benthos : These are bottom dwellers with little (sessile) or no movement (sedentary). They are mostly invertebrates living
on the substratum. e.g. annelid worms, bivalves, gastropods etc., benthos are of two types i) phytobenthos and ii)
zoobenthos.
Detritus : It is the dead and decayed organic matter of both plant and animal origin. Decomposing bits of leaves, twigs,
barks, water plants and animals form detritus. It can be in particulate or suspended form associated with rich microbial flora
and fecalmatter.
1.1.3 Classification of food based on its importance
Main or basic food : Food which is normally eaten by the fish or the most preferred food is the main food.
1. Occasional or secondary food : When the main food is not available, fish feed on other available food
temporarily. This type of food is called occasional or secondary food.
2. Incidental food: This type of food that occasionally enters the gut of a fish along with main food items.
3. Emergency or obligatory food :This is the one which fish takes in the absence of basic food to maintain
physiological activities. It is taken when there is no alternative food available.
Fishes are categorized based on their dependence on food type, preference,position in water column and feeding types.
Dependence on food type :In nature, the type of food available does not remain the same throughout. Therefore, fish may
change over to other available food or restrict to a limited type and the fishes are classified as:
1. Euryphagic : Fishes feeding on a mixed diet with no preference to any certain type.
2. Stenophagic :Fishes feeding on limited kinds of food.

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3. Monophagic :Fishes consuming only one kind of food.
1.2 Fish food preferences
1.2.1 Food preference
Depending on the food they take fishes are classified as the following:
1. Herbivorous :A number of fishes feed on unicellular algae, filamentous algae, and also higher aquatic plants. If the
plant material in the diet is 75% or more the fishes are considered to be herbivorous. i.e. Labeo fimbriatus, L.
rohita, Ctenopharyngodon idella,Oreochromis mossambicus .
2. Detritivorous :Those feeding mainly on detritus i.e. Labeo calbasu,Mugil cephalus.
3. Omnivorous :Those feeding on both plant and animal matter. The food of these fishes consists of varying
percentage of plant and animal matter and they form a link between herbivorous and carnivorous fishes. i.e.
Etroplus suratensis,Cyprinus carpio, Torputitora, Cirrhinus mrigala, Clariasbatrachus,Heteropneustesfossilis.
4. Planktivorous :Feeding mainly on plankton both phyto and zooplankton i.e. catla - zooplankton feeder ,silver
carp - phytoplankton feeder.
5. Carnivorous :Feeding on prey organisms. The examples of carnivorous fishes are: Wallago attu, Mystussinghala,
Channa striatus.
The carnivorous fishes may be:
a. Insectivorous:Mainly feeding on insects. i.e. Trout.
b. Carcinovorous:Mainly feeding on crustaceans. i.e. Black bass
c. Malacovorous: Feeding mainly on molluscs like snails/clams i.e. Black carp
d. Piscivorous:Feed on fish other than its own species. But, generally they prey upon small fishes of other
species rather than their own i.e. Barracuda.
e. Larvivorous:Feeding mainly on insect and crustacean larvae/fish larvae. i.e. Gambusia affinis.
f. Cannibalistic: Feeding on the young ones of the same species i.e. Channa marulius, Lates calcarifer.
1.2.2 Position in water column
Depending on the position in the water column they occupy, the fishes are categorized as:
1. Surface feeders :Fishes which live in the surface and feeding mostly on the food available in the uppermost layer
of water. e.g. catla feeding on zooplankton and silver carp feeding on phytoplankton.
2. Mid-water or column feeder :Fishes which live in the mid water or column water and feeding in the middle layer
are called mid-water or column feeders. e.g. rohu feeds on plant matter including decaying vegetation.
3. Bottom feeders :Fishes which live at the bottom and feed on the benthic fauna. e.g. mrigal feeds on detritus and
decaying vegetation and common carp on molluscs and chironomids in the bottom mud.
In composite fish culture, these feeding habits of fishes are advantageous to utilize the available food in water body.

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1.3 Major fish feeding types
1.3.1 Predator
Predator fish are the one which feed on macroscopic animals. These fishes have well developed teeth for grasping and
holding to seize their prey organism firmly. The predatory fishes have large mouth, reduced gill rakers,fairly large stomach
and short intestine. The stomach is provided with acid secretions to digest the proteinaceous food material. (e.g. ribbon fish,
seer fish, barracuda etc.). Normally predators feed during the day time and while requires acute vision. But in case of deep
sea predators,eyes are not well developed, so they locate their prey by smell, taste,touch and by lateral line sensory system
and chase with large gaping mouth.
1.3.2 Grazers
Grazing type of feeding is comparable to grazing behavior of cattle and sheep. Grazing fishes take their food by bites on a
large spread of food organisms. The grazers normally go in groups i.e. Butterfly fishes (Chaetodontidae) and Parrot fishes
(Sparidae) which are seen in coral reefs,feeding on coral polyps and on algae among the reef. Lepidophagus grazing is a
special type of grazing where the fishes pluck the scales from other fishes. i.e. Cichlids. In hatcheries some fishes exhibit
strange type of graze-feeding behaviour. i.e. Trout and Salmon tear off body parts from other fishes especially fins. In such
fishes, mouth is pointed and provided with plucking incisors.
1.3.3 Food strainers
They strain or sieve water to get the food material for which their gill rackers are modified. The gill rackers are numerous,
elongated and closely set in. With the help of such gill rakes,they filter large volume of water to obtain small sized
planktonic organisms. In plankton feeders,the food is selected by size not by kind or type i.e. Sardine, Silver carp and
Mackerelfeed on copepods, but they may take other plankton of the size of the copepods.
1.3.4 Food suckers
This type of feeding habits is seen in the case of bottom dwelling fishes. Here the fishes swallow their food by sucking the
desired food or food containing material. In such fishes, lips are modified for sucking purpose. They suck food by either
segregating the food before sucking in or ingest along with unwanted materials into the mouth and segregate it inside the
mouth e.g. sturgeon. On account of sucking habit many demersal fishes accumulate unwanted food material in large
quantities in the stomach e.g. catfish
1.3.5 Parasitic feeding
Parasitism is a specialized mode of feeding and fishes are no exception to this highly evolved feeding habit. The parasitic
fishes, feed on the body fluids of the host fish. Here the mouth is well developed and adapted to hold on to the host and
pierce and suck the body fluid. e.g. lampreys and hag fishes have terminal mouth which is surrounded by short barbles to
pierce the host fishes. Interestingly, in deep sea angler fish (Ceratias),males which are smaller in size are parasitic on the
large bodied female fish. Shortly after hatching, the male finds a female and attaches by its mouth to female are body and
the female responds by developing a fleshy papilla, from which the male can absorb nutrients. Once attached to the papilla,
the male takes no free living food at all.
1.4 Feeding adaptations in fishes
1.4.1 Feeding adaptations

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The diversity in feeding habits of fishes is the result of structural adaptations. The structural adaptations for specialized
feeding are seen in relation to lips, mouth, teeth, gill rackers,digestive tract and sensory organs.
1.4.1.1 Lips
Among fishes, there are Jawed (Gnathostoma) and Jawless (Agnatha) fishes. In jawless parasitic lampreys
(Petromyzontidae) and hag fishes (Myxinidae), the suctorial mouth serves as hold fast organs for attachment to the host and
as food remover from the host. In jawed fishes, the mouth is terminal for biting the food. The fishes which take large piece
of food at a time do not have modified lips (all carnivorous fishes. Suctorial feeders (suckers) have an inferior mouth and
fleshy lips. The lips of Sturgeons and suckers are mobile and described as plicate (having folds) or papillose (having small
tufts of skin or papillae). Lips not only help in feeding but they act as hold fast organs in rapidly flowing mountain stream
e.g. loaches. In addition, the suctorial feeders also have barbels around the mouth. The sensory organs present in these
barbels help in locating the food.
1.4.1.2 Mouth
Among the grazers and suctorial feeders, there exist not only specially developed lips but also adaptations on other mouth
parts. The trumpet fishes (Aulostomidae), the cornet fishes (Fistulariidae) and the pipe fishes (Syngnathidae) as well as
many butterfly fishes (Chaetodontidae) of coral reefs have mouth that resembles elongated beak. With elongated tube-like
mouth, feeding in the case of trumpet fishes may be by suction and in cornet fishes and Pipe fishes, it may be selective
grazing action with sharp teeth. In butterfly fishes, the long snout enables to reach into small cervices of the corals for
picking the food.
Predator fishes such as the Dories (Zeidae), certain Wrasses (Labridae) and the European bream (Cyprinidae) can form
temporary tubes which help in swallowing their prey from close range by forward extension of the jaws. A peculiar
modification of jaws is shown by the half beaks (Hemiramphidae), in which the lower jaw projects into a beak while upper
jaw is small, as a result mouth opening lies above. Owing to this modification, the beak helps in feeding at the surface of
water.
1.4.1.3 Teeth
These are the major structures showing outstanding modifications for feeding. In bony fishes there are three sets of teeth in
jaws, mouth and pharynx. Teeth in the jaws are those on the maxillary and pre-maxillary (upper jaw) bones, and on the
dentaries below (lower jaw bone). On the roof of the oral cavity, teeth are borne by the vomer, palatine and ecto-pterygoid
bones on each side. On the floor of the mouth, often tongue has teeth on it. Similarly, the teeth in the pharynx occur as pads
on various gill arch elements in many species (Cyprinidae, Catostomidae). Many predatory fishes have teeth like
modifications on the inner surface of the pharyngeal arch e.g. northern pike (Esox lucius).
Based on their shape and location, teeth in jaw are canine (fang like), incisor (frontline cutting), molariform (grinding with
flattened surface),cardiform (short, fine and pointed arising from a pad), and villiform (elongated teeth that resembles the
intestinal villi).
There is a strong relation between dentition, feeding habit and the food eaten by fishes. Predators such as barracuda,ribbon
fishes, silver bar have sharply pointed teeth which help in grasping, puncturing and holding the prey. In skates (Rajidae)
and in drums (Sciaenidae), there are grinding (Molariform) teeth in oral or pharyngeal cavities. They feed on snails, clams
and hard bodied crustaceans. Razor like cutting teeth (Incisors) are seen in predacious fishes like piranha of the Amazon

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and barracuda of warm seas. Teeth are generally absent in plankton feeders and in some of the more generalized
omnivores.
1.4.1.4 Gill Rackers
The gill rackers arise from gill arch which supports the gill filaments. They also protect the tender gill filaments from
abrasion by the ingested materials that are coarse in texture. The gill rackers are specialized in relation to food and feeding
habits. In plankton feeders, the gill rackers are numerous, elongated and closely set in for straining the water efficiently. In
many predatory fishes, which feed on larger prey, the gill rackers are reduced or absent. Fishes which have intermediate
feeding habit, the gill rackers are of moderate size.
1.4.1.5.1 Oesophagus
Oesophagus is a highly distensible muscular tube which can accommodate anything that a fish has ingested.
1.4.1.5.2 Stomach
It shows various modifications especially with respect to shape. In piscivorous fishes, the stomach is typically quite
elongate e.g. gars and barracuda. In omnivorous species, the stomach is sac like. In some fish, stomach is modified into
grinding organ and reduced in size, but the inner wall is greatly thickened and muscularized like a gizzard e.g. mullets,
sturgeons, gizzard shads. In fishes which devour a huge meal, the stomach is highly distensible, as in Bombay duck. A
remarkable modification of stomach exists in the puffers (Tetraodontidae) and porcupine fishes (Diodontidae) which inflate
it with water or air to assume an almost globular shape.
True stomach is not seen in all the fishes. In roach, a plant eating cyprinid, the oesophagus directly leads to intestine, so
also in parrot fishes. True stomach is also absent in plankton feeders. The presence or absence of stomach is not related to
feeding habit but to whether or not the fish have structures for grinding or triturating the food.
1.4.1.5.3 Intestine
The absorption of food material takes place in intestine. The length of intestine is shorter in carnivores and much elongated
and arranged in many fold in herbivores (very long and highly coiled in rohu and mrigal while the omnivores show an
intermediate condition.
1.4.1.6 Stimuli for Feeding
Two kinds of stimuli are involved in feeding:
1. Factors affecting the internal motivation or drive for feeding include season,time of day, light intensity, time and
nature of last feeding, temperature and any other internal rhythms that may exist.
2. Food stimuli perceived by the senses like smell, taste,sight and the lateral line system that release and control the
momentary feeding act. The interaction of these two groups of factors determines when, what and how a fish will
feed.
1.5 Detection of Food in Fishes
1.5.1 Detection of Food
Fishes are able to detect food by both physical and chemical senses by sensory organs which orient the fish towards food.
Based on the sensory responses,fishes are categorized as:
Night feeders :Detecting the food by smell and taste e.g. catfishes.

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Sight feeder :The fishes are active during the day time and their vision and position of eyes is important in the feeding
habit. Sight feeders feed intensely during day but it does not mean that they don’t feed at during the night. In surface
feeders like minnows, eyes are oriented upwards above the mid lateral line. This gives better view of objects at the surface
of water. In bottom feeders like cat fishes, the eyes are present below the mid lateral line and they can able to see the
bottom area better. The fishes which feed during day as well as at night have well developed lateral line that helps in
detection of food. Lateralline system is well developed in blind cave fishes and deep sea fishes. Other senses such as
olfaction and taste also play a role in locating the food available at a distance. Many fishes which feed by sight have acute
olfaction. Gustatory sensation enables the fish in the final selection and swallowing the food. The taste buds are
concentrated in the mouth, barbels, snout and sometimes on the lips.
1.5.2 Selection of food
Not all the food materials that enter the mouth are swallowed by the fish. The final selection takes place in the mouth and
pharynx especially in bottom dwelling fishes. These fishes feed on extraneous matter and it is subjected to selection inside
the mouth. This selection is made by various sensory structures situated in mouth, tongue, gill rackers,epibranchial organs,
and tissue surrounding the pharynx. The unwanted material is thrown out and in many instances unwanted food is also
thrown out from the gill openings. In some cases,they throw the unwanted food by coughing action. Normally gill rackers,
pharyngeal teeth, bristles and epibranchial organ serve as mechanical structures in retaining or rejecting the food.
1.5.3 How Much Food, Fishes Feed On?
Generally herbivores and plankton feeder are continuous feeders and they feed all through the day unlike carnivores. Food
of plant origin has poor nutritional protein content but more water and high fiber. In order to balance the nutritional
requirements, herbivores have to feed on large quantity e.g. grass carp. Conversely,the carnivores feed on animal matter
which is rich in nutrients; hence they take a small meal. Even in some carnivores, the nature of food varies; most of the
bottom carnivores feed on crustaceans and mollusks which have more indigestible matter in the form of shells. So their
intake is larger as compared to piscivorous fishes.
1.6 Fish Feeding Periodicity in Fishes
1.6.1 Feeding periodicity and variations
Depending on the quantity of food consumed, the frequency of feeding varies from few hours to 4-6 days e.g. deep sea
fishes. Small feeders have more feeding frequency. In addition, the factors regulating the feeding periodicity are:seasons,
migratory cycles, reproductive activity, age and size of fish.
1.6.1.1 Season
Seasons influence feeding frequency especially in temperate waters. Feeding periodicity is related to water temperature and
metabolic rate. Annual cycle of temperature variation is more pronounced in temperate waters, where feeding frequency is
more in summer.
1.6.1.2 Migratory cycle and reproductive activity
In temperate waters,some fishes exhibit feeding patterns in relation to migration. The fishes which undertake migration for
breeding eat intensively and accumulate reserve food material which enables development of gonads e.g. salmon. The
younger fishes are more active so they feed more than the older ones.
1.6.1.3 Amount of food consumed daily
Amount of food consumed daily depends mainly on the quantity of food and size of fish.

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1.6.1.4 Quantity of food
The amount of food consumed is related to metabolic rate which is in turn closely related to the temperature. In tropical
waters,temperature being higher the metabolic rate and food requirement is also higher. Therefore,fishes living in tropical
water feed on large quantity of food e.g. tuna. The fishes living in temperate waters feed on small quantity of food as the
temperature is lower and the metabolic activity is also low e.g. Salmon.
1.6.1.5 Size of fish
Small fishes consume more food when compared to large sized fishes. This is related to body weight. For example, small
fishes which weigh about 2-5 grams consume 6-10% of their body weight per day, whereas bigger fishes which weigh
about 30 gm or more feed on 2-3% of their body weight per day. The rate of consumption is also related to the condition of
the fish. In diseased fishes the rate of consumption is very low. During spawning season, most of the fishes stop feeding
due to the enlargement of gonads. Interestingly, european eel (Anguilla) stops feeding after maturation as a result, digestive
system degenerates and finally it dies after spawning.
1.7 Food and Feeding Habits of Fin Fishes in Indian Water
1.7.1 Indian Oil Sardine
It is predominantly a phytoplankton feeder,feeding mostly on diatoms like Fragillaria oceanica,Coscinodiscus,
Thallassiothrix and Pleurosigma. However, F. oceanica is the most favourite food item. In addition to diatoms, they may
also feed on copepods, dinoflagellates, ostracods, larval prawn, larval bivalves, fish eggs and some blue green algae. The
presence of diatoms, Fragillaria oceanica in large numbers indicates the abundance of oil sardine in coastal waters.
1.7.2 Lesser sardines
Lesser sardines feed on a variety of phytoplankton and zooplankton. Phytoplanktonic organisms include biddulphia,
coscinodiscus,thallasiothrix, fragilaria, nitschia, pleurosigma and zooplanktonic organisms include dinophysis,
peridinium, caratium, copepods,mysis, lucifer,larvae of prawns and crabs, fish eggs, acetes,fish and bivalve larvae,
crustacean larvae and molluscan larvae. e.g. Sardinella gibbosa, S. fimbriata, (fringe-scale sardine), S. albella (short-bodied
sardine), Amblygaster sirm (spotted sardine), S. dayi, S. clupeoides (smooth belly sardine), S. melanura (black-tipped
sardine), S. sindensis (kowala coval), White sardine and Dussumieria acuta, (common sprat).
1.7.3 Anchovies
Anchovies feed on phytoplankton, viz. diatoms, dinoflagellates and zooplankton viz. copepods, acetes,ostracods,
cladocerans, amphipods and euphausiids. The crustacean plankton accounts for about 60%. e.g. Encrasicholina punctifer,
E. devisi, Stolephorus bataviensis,S. commersonii, S. indicus and S. baganensis
1.7.4 Mackerels
Mackerels are plankton feeders, feeding to a greater extent on zooplankton (cladocerans, ostracods, larval polychaetes etc.)
and to a lesser extent on the phytoplankton. Adults feed on larval shrimps and fish. e.g. Rastrelliger kanagurta (Indian
mackerel), R. brachysoma (short mackerel) and R. faughni (island mackerel).
1.7.5 Tuna

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Tunas are carnivores and the major food items include crustaceans (larvae, juveniles and adults of shrimps and crabs),
cephalopods (juveniles and adults), eggs, larvae and juveniles of small fishes. e.g. Euthynnus affinis (little tuna), Auxis
thazard (frigate tuna), A. rochei (bullet tuna), Katsuwonus pelamis (skipjack tuna), Thunnus tonggol (long tail tuna), T.
albacores (yellow fin tuna) and Sarda orientalis (striped bonito), Gymnosarda unicolor (dogtooth tuna) and Thunnus
obesus (big eye tuna).
1.7.6 Carangid fishes
Carangids feed mostly on fishes like anchovies, sardines, silver bellies, squids, cuttlefishes shrimps and crabs. The young
ones feed mostly on prawns, squids and anchovies. e.g. Alectis indicus (indian thread-fin trevally), Alepes kalla (trevally),
Atule mate (one-finlet scad), Caranx sexfasciatus (dusky trevally), C. carangus (black-tailed trevally), C. ignobilis (yellow
fin trevally), C. melampygus (blue fin trevally), Coryphaena hippurus (dolphin fish), Carangoides armatus (long fin
trevally), C. malabaricus (malabar trevally), C. chrysophrys (long-nose trevally), Decapterus russellii (round-scad),
Selaroides leptolepsis (yellow-strip trevally), and Trachinotus blochii (sub-nose pompano).
1.7.7 Ribbon fishes
All the ribbon fish species are highly carnivorous, predatory and voracious feeders, feeding both during day and night.
They prefer small and medium sized fishes and shrimps. e.g. Trichiurus lepturus (grey ribbonfish), T. gangeticus (ganges
hair tail), Lepturacanthus savala (silver ribbonfish) and E. glossodos (long tooth hair tail).
1.7.8 Bombay-Duck
It is carnivorous and to some extent cannibalistic. It feeds on golden anchovy, juveniles of its own species, and non-penaeid
prawns.
1.7.9 Silver belly
Silver bellies are mainly zooplankton feeders. e.g. Leiognathus dussumieri, Secutorindicus, Gazza minuta
1.7.10 Sciaenids
Sciaenids are carnivores and active predators. Young ones feed on crustaceans, especially prawns and adults feed on fishes.
They also feed on molluscs, echinoderms, annelids etc. to certain extent. e.g. Otolithes cuvieri, O. cuvieri, O. ruber,
Johnius glaucus, J.carutta. Protonibea diacanthus, Johnieops macrorhynus, Nibea maculate.
1.7.11 Lizard fishes
The young ones feed chiefly on crustaceans like lucifer, acetes, mysis and fishes such as anchovies and silver bellies. The
adults feed mainly on prawns and fishes such as anchovies and silver bellies. They also feed on small amount of copepods,
cirripid larvae, and larval forms of crustaceans. e.g. Saurida tumbil (brush toothed lizard fish), Trachinocephalus myops,
Saurida longimanus (long fin lizard fish) and S. micropectoralis (short fin lizard fish)
1.7.12 Pomfrets
Young ones feed on copepods ostracods, amphipods, larval stages of squilla, lucifer and filamentous algae mainly
Trichodesmium spp. Adult feed on crustaceans such as copepods (Oithona spp., Euterpina spp., and Eucalanus spp.),

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copepod nauplii, ostracods, amphipods, lucifer and zoea larvae. They also feed on larger crustaceans, polychaetes, larval
decapods, foraminiferans, and Sagitta spp. This species has different feeding habits at different depths. e.g. black pomfret
(Parastromateus niger), silver pomfret (Pampus argenteus) and chinese pomfret (Pampus chinensis).
1.7.13 Goatfishes
Goatfishes are carnivores. They feed almost exclusively on crustaceans, especially penaeid shrimps, crabs and small fishes.
e.g. Mulloides flavolineatus, M. vanicolensis, Parupeneus bifasciatus, P. indicus, P. barberinus, P. macronema, P.
cinnabarinus, P. cyclostomus,Upeneusmoluccensis, U.sulphureus,U. vittatus, U. oligospilus, U. bensasi, U. sundaicus,
U.tragula and U. taeniopterus.
1.7.14 Perches
Perches are predatory fishes, mainly feeding on other fishes and invertebrates such as crabs, prawns, stomatopods etc.
Cephalopods are also seen in the diet of some perches. e.g. order: perciformes – include families such as serranidae (rock
cods/groupers), lutjanidae (snappers), lethrinidae (pig face breams), nemipteridae (threadfin breams), haemulidae (grunts),
caesionidae (fusiliers), priacanthidae (bulls eye), acanthuridae (surgeon fishes) and siganidae (rabbit fishes).
1.7.15 Flatfishes
In general, the food items of flatfishes include in benthic invertebrates, fishes and cephalopods. The malabar sole prefers a
diet of polychaetes, amphipods and small bivalves. P. erumei is a carnivore, feeding predominantly on fishes and
cephalopods with crustaceans and bivalves constituting the subsidiary food. e.g. bothidae (flounders), cynoglossidae
(tongue soles), psettodidae (indian halibut) and soleidae (soles).
1.7.16 Elasmobranches
Elasmobranches are carnivores and predaceous in nature, with the exception of Rhincodon typus (Whale Shark) which is
mainly a zooplankton (filter) feeder. Sharks mainly feed on pelagic teleosts such as sardine, mackerel, bombay duck etc.
and cephalopods (squid, octopus, and cuttlefish). Skates and rays mostly feed on benthic organisms viz. crustaceans,
molluscs, polychaetes, amphipods and smaller fishes. e.g. sharks, skates and rays belonging to the families carcharhinidae,
hemiscylliidae, rhincodontidae, sphyruidae, stegostomatidae, hemigaleidae, ginglymostomatidae, pristidae, myliobatidae,
and dasyatidae.
1.8 Food and Feeding Habits of Shell Fishes in Indian Water
1.8.1 Penaeid shrimps
Penaeid shrimps are mostly omnivorous, feeding at the muddy bottom. Their post-larvae and juveniles feed on detritus but
sub-adult prawns prefer polychaetes, bivalves, gastropods, benthic copepods, ostracods, amphipods and foraminifers. The
adults of larger penaeids become predaceous and feed on cephalopods and smaller species of prawns and fishes. e.g.
Fenneropenaeus indicus (Indian white prawn), P. semisulcatus (Green tiger prawn), P. monodon (Giant tiger prawn), P.
merguiensis (Banana prawn), P. japonicus (Kuruma prawn), P. penicillatus (Red-tail prawn), Metapenaeus dobsoni
(Flower-tail prawn), M. monoceros (speckled prawn), M. affinis (Jinga prawn), M. kutchensis (Ginger shrimp), M.
brevicornis (Yellow prawn), Parapenaeopsis stylifera (Kiddi prawn), P. hardwickii (Spear prawn), P. sculptilis (Rainbow

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prawn), P. maxillipedo (Torpedo prawn), P. uncta (uncta prawn), Tranchypenaeus curvirostris (Rough prawn),
Metapenaeopsis stridulans (Fiddler shrimp), Parapenaeus longipes (Flaming prawn), Solenocera crassicornis (Coastal
mud prawn) and S. choprai (Coastal mud prawn).
1.8.2 Non-penaeid shrimps
Non-penaeid shrimps mainly feeds on detritus consisting of fibrous and granular material of phyto and zooplankton origin.
Nematopalaemon tenuipes feeds mainly on the planktonic crustacean. Exhippolysmata ensirostris is highly predaceous and
feeds on Acetes, polychaetes and young ones of fish and shrimps. e.g. Acetes indicus (jawala paste shrimp),
Nematopalaemon tenuipes (spider prawn) and Exhippolysmata ensirostris (Hunter shrimp).
1.8.3 Marine crabs
Crabs feed mainly on smaller crustaceans, fishes, molluscs, polychaetes, detritus, bits of plant and other organic materials.
e.g. Portunus sanguinolentus, P. pelagicus, Charybdis feriatus, C. annulata and C. natator.
1.8.4 Lobsters
Lobsters generally prefer mussel and clam. Occasionally, they eat smaller crustaceans, polychaetes, fishes while
scavenging. e.g. Panulirus polyphagus, P. homarus, P. ornatus, P. longipes, P. versicolor and Thenus orientalis
1.8.5 Cephalopods
The cephalopods are generally carnivorous and their food consists of teleost fishes, crustaceans and other cephalopods.
Cannibalism is common among cephalopods. Feeding intensity decreases during the spawning season. e.g. Sepidae (true
cuttle fishes), Sepiadaridae (bottle tail squid) and Sepiolidae (bobtail squid).
2. Gut Content Analysis
2.1 Gut Content Analysis in Fishes
2.1.1 Gut Content Analysis in Fishes
Direct observation on the feeding habits of a fish in its natural habitat is nearly impossible and therefore to ascertain the
nature of a fish food, the best way is to examine its gut contents. The study of feeding habits of a fish is based on gut

11
content analysis which is a standard practice. Stomach content analysis provides important insight into fish feeding patterns
and their quantitative assessment. Accurate description of diets and feeding habits also provides the basis for understanding
trophic interactions in aquatic food webs. The gut analyses lucidly unravel the trends in the seasonal, geographical and
spatial variations in the dietary composition of fish and the diurnal rhythm in feeding behavior.
The analysis of the different food items is difficult as the food items are normally found in a crushed or semi-digested
condition.
2.1.2 Limitations of gut content analysis
1. A fish when captured or when preserved in formalin for study, often vomits the remains of its last meal as a result
of the chemical shock
2. Whatever material is found in the gut, cannot be considered as food
3. Other methods such as morphological (position of mouth, relative gut length, etc.) and environmental (food
spectrum in the aquatic system) evidences should be calculated for verification and confirmation of the gut analysis
data.
Separation of gut content
The region between the oesophagus and the pyloric sphincter in the alimentary canal forms the stomach. To study the food
habits of fishes, the total length of the fish, the body weight of the fish, sex, feeding intensity, the stage of sexual maturity
of the fish has to be recorded. The stomach should be removed from the fish and it should be preserved in 5 % formalin,
dried between sheets of filter paper and slit open with a pair of scissors. If the stomach appears empty or contains only
traces of food (less than 1.0 mg), it is rinsed with water directly into a petri dish. If it contains a weighable quantity of food,
the excess water is removed using absorbent tissue paper. The contents of the stomach are then weighed and washed in
petri dish and examined under a microscope. The food items are identified and sorted into various taxonomic groups and
the numerical percentage is estimated. Usually fragments of crustaceans (e.g. appendages),polychaetes (e.g. setae),
molluscs (e.g. radula, mandible, shell parts) are counted as full animals however depending upon the type of fragments, the
scaling of animals to left to researches. Before fixing in formalin, the intensity of feeding has to be recorded.
2.1.3 Feeding intensity
1. Gorged stomach: A stomach in which the gut contents are full and occupy the entire stomach. The wall of
stomach appears transparent and organisms inside the stomach could be seen.
2. Full stomach: A stomach in which the food items occupying the entire cavity of the stomach.
3. ¾ Full Stomach: A stomach in which the food items occupying ¾ of the stomach
4. ½ Full Stomach: A stomach in which the food items occupying ½ of the stomach
5. ¼ Full Stomach: A stomach in which the food items occupying ¼ of the stomach
6. Trace stomach: Very little or few organisms are present in the stomach
7. Empty stomach: There will be no food item in the stomach. A little digested secretion may be present. Wall of the
stomach is highly shrunken.
8. Regurgited stomach: There will be no food item in the stomach. Wall of the stomach is shrunken.
2.2 Methods of Gut Content Analysis
2.2.1 Methods of fish content analysis

12
Fish diets can be measured in a variety of ways, and methods of gut content analysis are divided into two categories, viz.,
quantitative and qualitative. The quantitative method is the measure of quantity of gut content and is of three types, viz.,
numerical, gravimetric and volumetric. The qualitative analysis consists of complete identification of the organisms in the
gut contents. Many authors consider volume or weight as more satisfactory method for quantitative analysis of gut
contents. Hynes (1950) proposed volumetric method as a very suitable means of assessment especially in case of
herbivores. The methods of quantification generally followed in food studies are outlined below.
2.2.1.1 Occurrence method
 The number of stomachs in which a particular food item (i.e. a particular species) as a percentage of the total
number of stomachs is determined. [or]
 The frequency of occurrence (i.e. the number of times of occurrence) of all the food items among the stomachs
examined is summed and the frequency of occurrence of each diet expressed as a percentage of the total number of
specimens examined.
Stomachs Fish Crab Mollusc Plant Shrimp Total
1 √ √ √ √ 4
2 √ √ √ 3
3 √ √ √ 3
4 √ √ √ √ 4
5 √ √ 2
6 √ √ √ √ 4
7 √ √ √ 3
8 √ √ √ 3
9 √ √ √ 3
10 √ √ √ 3
Total 10 7 4 5 6 32
Fish = Number of stomachs in which fish occurred / Total number of stomachs
= 10/10*100 = 100 %
Crab = 7/10*100 = 70 %
Mollusc = 4/10*100 = 40 %
Plant = 5/10*100 = 50 %
Shrimp = 6/10*100 = 60 %
2.2.1.2 Numerical method
The total number of individuals of each food item is recorded and expressed as percentage of the total number of food
organisms in the stomachs examined.
Stomachs Fish Crab Mollusc Plant Shrimp Total
1 2 1 2 3 2 10
2 3 2 1 1 2 9

13
3 2 1 2 2 1 8
4 1 1 0 3 2 7
5 5 1 0 1 0 7
6 1 3 3 0 0 7
7 2 1 1 1 0 5
8 4 4 0 0 1 9
9 1 2 2 0 2 7
10 3 0 1 1 1 6
Total 24 16 12 12 11 75
Fish = Number of fish observed in the stomachs / Total number of food items*100
= 24/75*100 = 32.00 %
Crab = 16/75*100 = 21.33 %
Mollusc = 12/75*100 = 16.00 %
Plant = 12/75*100 = 16.00 %
Shrimp = 11/75*100 = 14.66 %
2.2.1.3 Volumetric method
Volume of each food item is determined by the displacement method and expressed as a percentage of the total volume of
the stomach contents. Volumetric and gravimetric methods are the best method.
Stomachs Fish (cm3
) Crab
(cm3
)
Mollusc
(cm3
)
Plant
(cm3
)
Shrimp
(cm3
)
Total
(cm3
)
1 2 1 2 3 2 10
2 3 2 1 1 2 9
3 2 1 2 2 1 8
4 1 1 0 3 2 7
5 5 1 0 1 0 7
6 1 3 3 0 0 7
7 2 1 1 1 0 5
8 4 4 0 0 1 9
9 1 2 2 0 2 7
10 3 0 1 1 1 6
Total 24 16 12 12 11 75
Fish = Volume of fish in the stomachs/Total volume of stomach contents*100
= 24/75*100 = 32.00 %
Crab = 16/75*100 = 21.33 %
Mollusc = 12/75*100 = 16.00 %
Plant = 12/75*100 = 16.00 %

14
Shrimp = 11/75*100 = 14.66 %
2.2.1.4 Gravimetric method (Based on weight)
Total weight of all food items is determined. Weight of each food item is expressed as a percentage of the total weight of
stomach contents. It may be done by wet weight or dry weight. The dry weight is determined by drying the food items in an
oven at 60 – 80°C until a constant weight is obtained and then weighing the dried matter. The wet weight is determined by
removing the excess water by removing the surface water by blotting them on tissue paper and then weighing.
Stomach Fish (g) Crab (g) Mollusc (g) Plant (g) Shrimp (g) Total (g)
1 2 1 2 3 2 10
2 3 2 1 1 2 9
3 2 1 2 2 1 8
4 1 1 0 3 2 7
5 5 1 0 1 0 7
6 1 3 3 0 0 7
7 2 1 1 1 0 5
8 4 4 0 0 1 9
9 1 2 2 0 2 7
10 3 0 1 1 1 6
Total 24 16 12 12 11 75
Fish = Weight of fish in the stomachs/Total weight of stomach contents*100
= 24/75*100 = 32.00 %
Crab = 16/75*100 = 21.33 %
Mollusc = 12/75*100 = 16.00 %
Plant = 12/75*100 = 16.00 %
Shrimp = 11/75*100 = 14.66 %
2.2.1.5 Points method
Points are given to each food item. The number of points depends on whether the organism is very common in the stomach
contents (highest number of points) or rare (lowest number) and the size of the organisms (i.e. one larger organism is
counted as equal to a large number of small ones). Each category is then allotted a number of points and all the points
gained by each food item are summed and expressed as percentage of the total points. It is rapid, easy and requires no
special apparatus; with experience, this method could be very accurate.

15
Points Method Based on the Stomach Fullness
The stomach is opened and is described according to the amount of food it contained as: full, ¾ full, ½ full, ¼ full, less than
¼ full, empty or trace. Then according to the degree of fullness, it is allotted 100, 75, 50, 25, 12 or 6 points respectively.
The contents are then placed in a petri dish and the relative amount of each food item present is estimated visually. Points
are allotted to each category as a result of this visual estimation. For example, if a stomach ¾ full (75 points) contains a
mass of Leiognathus sp. and a mass of Penaeus sp. equalto about ½ the amount of Leiognathus sp. and Sepia sp. equalto
about ¾ of Penaeus sp.,then the allocation of 75 points would be: Leiognathus sp. 40; Penaeus sp. 20 and Sepia sp. 15.
Evaluation by points thus taken into account about the amount of food in the stomach as well as the number of organisms
consumed.
2.3 Indices of Gut Content Analysis
2.3.1 Index of Relative Importance: (IRI)
This index is useful in evaluating the relative importance of various food items. Based on the frequency of occurrence,
number and volume of each item, this can be determined by:
IRI = (% N + %V) %F
where, N = Numerical percentage
V = Volumetric percentage
F = Frequency of occurrence percentage
IRI for Fish = (32.00 + 32.00) 31.25 = 2000; 2000/4381.06*100 = 45.65 %
IRI for Crab= (21.33 + 21.33) 21.88 = 933.40; 933.40/4381.06*100 = 21.30%
IRI for Mollusc = (16.00 + 16.00) 12.50 = 400; 400/4381.06*100 = 9.13 %
IRI for Plant= (16.00 + 16.00) 15.63 = 500.16; 500.16/4381.06*100 = 11.42%
IRI for shrimp=(14.66 + 14.66) 18.75 = 547.50; 547.5/4381.06*100 = 12.50 %
------------------
Total = 4381.06
------------------
2.3.2 Absolute importance index: (AI)
This index of various food species (items) can be determined as follows:

16
AI = %F + %N + %W
Comparative Feeding Index
This is a combination of the points method and the relative importance method and depends on the volume, fullness and
frequency of each food item. This method involves the allotment of points to each food organism and the mean value per
fish is multiplied by the percentage of total fish sampled.
Index ofPreponderance
This index is a composite one based on the volume and the occurrence index. If Vi and Oi are the volume and occurrence
index of food item i (as indicated by their percentage),the combined index l for food i may be determined as follows:
li = ViOi / S ViOi *100
This is the best method
a. Volumetric Method: (V)
10 Stomachs Fish Crab Mollusc Plant Shrimp
Total 24 16 12 12 11
b . Occurrence Method: (O)
10 Stomachs Fish Crab Mollusc Plant Shrimp
Total 10 7 4 5 6
Fish (ViOi) = 24 x 10 = 240
Crab = 16 x 7 = 112
Mollusc = 12 x 4 = 48
Plant = 12 x 5 = 60
Shrimp = 11 x 6 = 66
---------
Total S ViOi = 526
---------
Fish = 240 / 526 *100 = 45.63 %
Crab = 112 / 526 *100 = 21.29 %
Mollusc = 48 / 526 *100 = 9.13 %
Plant = 60 / 526 *100 = 11.41 %
Shrimp = 66 / 526 * 100 = 12.55 %
2.3.3 Gastrosomatic Index: (GoSI)

17
GoSI = weight of the stomach / weight of the fish * 100
The gastrosomatic index sometimes indirectly indicates the spawning season in certain species of fin fishes. This index is
very low during the peak spawning season because of the more number of empty stomachs. The rise and fall of
gastrosomatic index always show an inverse relationship with the Gonadosomatic Index. This is mainly because in fully
matured fishes, the Kn value and Gonadosomatic Index are high.
3. Age and Growth
3.1 Age and Growth in Fishes
3.1.1 Age and growth in fishes
Growth is one of the basic characteristics of living organisms and which primarily increase in body size as a function of
age. It involves increment in size and enhancement of weight. In aquaculture, where juvenile fishes of known age are
reared, growth rate is easily determined with period of culture. But, such growth is influenced by a number of factors and it
does not truly represent the growth in natural wild fish populations. In natural water bodies, age and growth studies are
essential to understand the age structure of a population from which mortality rate is estimated. The mortality rate, in turn
enables to find out exploitation rate and subsequent management interventions of a commercially exploited stock. The
annual variations in fish catch rely upon growth pattern of the stock of a species. It is often desirable to segregate the fish
catch on the basis of age groups to understand the vulnerability of any specific age group to the fishing gear.
Growth in fishes can be determined by counting annual or daily rings that are formed on hard parts such as scales, otolith,
vertebrae etc. The annular rings are formed due to seasonal variations in temperature and availability of food in the
environment. Another direct method of recording growth is by tagging and recapture,but it is expensive and recovery of
tagged fishes is meager. In the case of crustaceans, t he only hard part is shell or exoskeleton which is shed periodically. So,
direct estimation of age and growth is not possible in crustaceans. However,severalindirect methods have been developed
which allow the conversion of length-frequency data into age composition.
3.1.2 Growth Model
One of the integral elements of the dynamics of fish population is growth. It can be expressed by mathematical models
which are employed to estimate size of a fish at given age. Mathematical expression of growth is necessary for integrating
it with the analytical models which are used for management of exploited fish stocks. The most widely used model for
growth is given by Von Bertalanffy (1938). The Von Bertalanffy Growth Function (VBGF) is expressed as:
Lt= L ∞(1- e-k (t- t
0
)
)
Where,‘L ∞’ is the maximum size that could be attained by a fish; it is also termed as asymptotic length. ‘K’ is a growth
coefficient at which fish attains the maximum length and ‘to‘ is a hypothetical age at which length of a fish is zero and ‘t’ is
time to reach the length Lt. These parameters of growth are integrated in dynamic pool models to know the optimum size of
a fish that can be harvested on sustainable basis.
3.2 Methods of Age Determination using Hard Parts
3.2.1 Scales

18
For age and growth study, 3-4 scales from the region between dorsal fin and lateral line are removed. They are cleaned
after removing extraneous matter and mucous by washing in tap water and rubbing between finger tips. To make scales
more clear and soft, they are dipped in weak solution (1%) of KOH for about 5-10 minutes, then washed in tap water and
dried in air and preserved as dry mounts.
Small sized scales are mounted between two glass slides and studied with the help of compound microscope or stereoscopic
binoculars at appropriate magnification through the eye piece fitted with oculometer. When the circuli are not clear in small
scales, they are stained with Alizarin Red S and mounted in glycerin for study. Large sized scales are kept in paper
envelopes in sunlight for about 5-6 hours to remove the moisture. The large scales are read under the microfilm reader and
their magnified images are observed on the screen at appropriate magnification. Lateral scale radius and the distance
between the focus and annuli are measured for a relationship between scale radius and fish length. By extrapolating the
regression line, a correction factor is calculated and the value so obtained is used for back calculations and the growth
parameters.
3.2.2 Opercular bones
It is easy to collect the opercular bones of the commercial fishes from the processing industries or fish markets. The
opercula should be detached from the skull and freed from extraneous muscles. These bones should be boiled in water for
about ten minutes and all muscles may be cleaned with a soft brush for 4-5 minutes. The annual rings become clear with
storage. Using black background, the opercular bones are observed under stereo-binocular microscope. Due to large size, it
is difficult to measure the opercular length and the annuli either under binocular microscope. Under such conditions, the
rings on the bone are marked and traced with pencil. The opercular length O-A,the annuli O-A1, O-A2,O-A3,….O-An are
measured and regression analysis of opercular length and fish length is carried out. The regression equation is used for
back-calculations. There is no correction factor in this case.
3.2.3 Vertebrae
The vertebrae lying below the dorsal fin (if two fins are present,then below the first dorsal) are removed and cleaned by
boiling in water for 10-20 minutes to remove muscles. Then they are soaked for several minutes in detergent, rinsed in tap
water and dried at 35˚ C. They can be stained with alizarin Red S, rinsed and air dried. There are two methods for
examining the annual layers.
a. The central point of a vertebra is examined under a stereoscopic binocular microscope.
b. The vertebra is cleaved length-wise in the dorso-ventral direction; half of the vertebra is fixed on wax so that the
flat side is directed upwards and examined under stereo-binocular microscope.
It is desirable to study large number of vertebrae for the clarity of rings before actually using the vertebrae in future studies.
3.2.4 Cleithra
Muscles are removed from cleithra either with a knife or by boiling them in water. The bones can be stored after drying in
ordinary envelopes, or kept indefinitely in air with virtually no deterioration in clarity of optical zonation. These can be
viewed under stereoscopic binocular microscope.
3.2.5 Otoliths
Sagitta, Lapillus and Asteriscus are the three otolith present in the membranous labyrinth of fish on each side. Of these,
sagitta is the largest and often used in age determination. The otoliths exhibit the best pattern of growth as calcium
resorption is not known in them. Their use has been found satisfactory in young and fast growing fishes.

19
Otoliths removed from the membranous labyrinth can be stored in glycerol and water in the ratio of 1:1 with a little thymol
added to the solution to prevent growth of bacteria and fungus. Ethanol can also be used in place of glycerol. It has been
reported that otoliths stored upto 5 years show no loss of clarity.
An otolith surface can be aged by immersing it in water and examining it under a dissection microscope using reflected
light. Some otoliths have a cloudy or chalky surface rendering the identification of the growth zones difficult. The zones
may be made distinct by rapidly dipping the otolith in a weak solution of HCl (usually 2%) before placing in water.
The otoliths of slow growing fishes become thick and the yearly growth zones are not formed equally on all sides. To
differentiate year marks, the study of cross sections is recommended.
Otoliths are ground on the medial side down to the level of margin on 400-500 grade carborundum stone or on ground glass
strip with 400 - 500 grade carborundum powder using dilute (1%) HCl as wetting agent. Creosote oil is also used as wetting
agent. The ground otoliths should be viewed under stereo-binocular microscope. For sectioning, the otoliths are dipped in
toluene to ensure that the epoxy will adhere to the structure. Sections are cut at 0.5mm thickness, or at any other thickness
which yields best results. Several sections from one structure are placed on a slide with fast drying liquid or mounting
material.
3.3 Methods of Age Determination Using Length Frequency Method
3.3.1 Length frequency method
In length frequency method or size frequency method, the basic principle is that the length frequency distributions tend to
group themselves around a central value called mode and the progression of modes through successive intervals of time
(e.g. month ) indicates the pattern of growth.
3.3.2 Collection and processing of length frequency data
1. Samples for length frequency should be collected at random from the commercial catches as soon as they are
landed. Sampling should be done before sorting into various market size groups.
2. Length data should be collected separately for different gears and for different mesh types of the same gear.
3. Length frequency data are to be recorded twice or thrice in a week from the landing centre.
4. While collecting the length data, sexes should be treated separately.
5. While recording the length data, total length or fork length or standard length should be taken depending on the
convenience. The data should be recorded in mm or cm in a primary register.
6. It is better to take the length frequency data for a period of two years (24 months).
7. Individual lengths are grouped into appropriate size classes which should not normally exceed twenty five.
8. The weekly data may be pooled on a monthly basis.
9. The data thus pooled must be drawn in the form of frequency polygons or histograms for each month.
10. Progression of modes is traced through successive months.
3.3.3 Integrated method (Pauly, 1983)
To calculate age and growth of fishes, Pauly’s integrated method can be followed. In this method, a growth curve is drawn
with a curved ruler directly upon the length frequency samples sequentially arranged in time. Alternatively, modes in the
length-frequency are plotted against time in successive month in the form of a scatter diagram. The progression of modes is
then traced from the origin of each brood to its maximum modal position. This method is based on the following tenets:
1. Growth in fishes is at first rapid, then decreases smoothly and for the population as a whole is best approximated
by a long continuous curve rather than by severalshort straight segments.

20
2. A single, smooth growth curve interconnecting majority of the peaks of sequentially arranged length-frequency
samples is likely to represent the average growth of the fishes of a given stock.
3. The growth patterns repeat themselves from year to year (which is also assumed when the “annuli” of otoliths are
counted). While drawing curves, the following points are to be noted.
4. The intervals on the time axis between the various samples must be proportional to the time elapsed between the
sampling dates.
5. The original data must be plotted at least twice or more along the time axis, which allows for longer, stabilized
growth curves to be drawn and all relevant age groups should to be included in one single line.
6. When severalgrowth curves are drawn (reflecting the production of severalbroods per year), the various growth
curves should have the same shape,and vary only as to their origin.
7. The scale of the ordinate (length) should start at zero, thus allowing to identify the approximate spawning periods.
8. Each growth curve must interconnect severalpeaks; the more peaks a curve connects the more likely to depict the
actual growth of a population.
9. The modal lengths corresponding to various ages (starting from an arbitrary age) can be read off the curve at
regular time intervals, and may be then used to determine the growth parameters.
4. Reproductive Biology
4.1 Reproduction in Fishes
4.1.1 Reproduction in fishes
Reproduction is a fundamental biological process which enables continuation of species. In fisheries biology, reproduction
assumes greater significance to understand sexual dimorphism, process of maturation, size or age of maturity, breeding
season, spawning area, sexual segregation, migration, fecundity, embryonic and larval development and recruitment. Most
of the management strategies in capture fisheries are based on reference points that are the manifestations of reproductive
biology. In aquaculture, knowledge of reproductive biology of a fish is essential for hatchery production of fish feeds.
4.1.2 Types of reproduction
In fishes, generally the sexes are separate exhibiting bisexual reproduction, but sometimes they are hermaphrodites and
rarely parthenogenesis is seen.
In bisexual reproduction, sperms and eggs are produced in male and female sex organs called testis and ovaries
respectively. In hermaphrodites, both the sex organs are in a single individual and may develop simultaneously; such fishes
are called synchronous hermaphrodites (e.g. Polynemus heptadactylus). But,they do not practice self fertilization. Most
hermaphrodites show development of male gonads before female gonads (protandrous hermaphrodites e.g. Sparus spp.)
while others show development of female gonads before male gonads (protogynous hermaphrodites Epinephalus
diacanthus) so as to achieve cross fertilization.
Parthenogenesis is development of young ones without fertilization. This is reported from a tropical fish, Poeilia formosa.
In parthenogenetic mode of reproduction mating with a male is required, but the sperm serves only one of its two functions,

21
that of inciting or triggering the egg to develop. It does not take any part in heredity. The resultant young ones are always
females (gynogenesis) with no trace of parental characters.
4.1.3 Male reproductive organ (Testis)
In case of male fish, the reproductive organ consists of a pair of testes which lies ventral to the kidneys in the posterior
region of the abdominal cavity. The testes remain attached to the body wall by mesorchia. The testes are free anteriorly but
posteriorly they continue as sperm ducts which open into urinogenital papillae. A testis consists of seminiferous tubules
which are lined by germ cells that produce spermatogonia. The spermatogonia undergo a number of maturation stages to
develop motile sperms. This process is called spermatogenesis. In the space between the seminiferous tubules there are
interstitial cells called Leydig cells, which are endocrine in function and produce male sex hormones called testosterone.
4.1.4 Female reproductive organ (Ovary)
In case of females, a pair of elongated sac like structures found in the abdominal cavity just ventral to the kidney which are
called ovaries. They are attached to the body wall by mesovarium. The ovaries are free anteriorly but each ovary continues
posteriorly as oviduct. Two oviducts fuse and open exteriorly by a genital aperture. The wall of the ovary consists of three
layers.
1. Peritoneum (outermost thin covering layer)
2. Tunica albuginea (made up of connective tissue, muscle fibres and blood capillaries)
3. Germinal epithelium
Germinal epithelium is the vital part in ovary where development of the eggs takes place. The germ cells in the germinal
epithelium are called oogonia which undergo a number of maturation stages to become a ripe ovum. This process is called
oogenesis.
Breeding :The term breeding refers to successive stages of courtship, mating and spawning.
Courtship: It is the heterosexual reproductive communication system which ultimately leads to mating. It is a process
during which mature males try to attract mature female or vice versa by displaying brilliant colour or by swimming around
the other. Sometimes mature males fight among themselves to attract the females. In case of Betta, the brilliant coloured
males swims around the female with his beautifully coloured fins fully extended and mouth widely opened and the
branchiostegal rays protruding out to expose the bright red gills.
Mating : It refers to the sexual act itself in which at least one male and one female come close together and release their
gametes more or less simultaneously into the surrounding media (external fertilization) or by the transfer of sperm from
male into female (internal fertilization).
Spawning
It is the process of release of gametes i.e. sperms and eggs from the sperm duct or oviduct respectively. There are two types
of spawning-
1. Oviparous: It is the process of emission or release of male and female gametes (sperm and eggs) from the body of
the fish to the exterior or outside.
2. Viviparous: Releasing of developing young ones to the external environments (In case of internal fertilization).
Fertilization
There are two types.
1. External fertilization: Eggs from female and milt (liquid containing sperm) from male are released
simultaneously to the exterior environment where they meet each other for fertilization.

22
2. Internal fertilization: Sperms are deposited into the reproductive organ of the female where fertilization takes
place . In case of internal fertilization following three things are usually found
(a) Fertilized eggs may be released (embryos) immediately after fertilization. or
(b) In some fishes, developed embryos (before hatching) are released. Here fertilization and incubation takes place inside
the fish.
(c) In some fishes, hatchlings come out (in live bearers).
Spawning Stages
Broadly, it can be categorized into three types. They are:-
1. Pre-spawning
2. Spawning
3. Post spawning
In pre-spawning, different stages of development of gonad (Testis and Ovary) takes place. During spawning stage,release
of sperms and eggs occurs. Post spawning stage is the recovery stage where maturation of gonads begins from the initial
stage.
Prior to the spawning, sperms are released into the sperm duct which is called spermiation. Similarly, the eggs are released
into the oviduct prior to spawning which is called ovulation.
The spawning behavior differs from species to species. Some fishes spawn only once and die. But some other fishes spawn
severaltimes in their life time. During pre-spawning stage gonads occupy maximum space in the viscera cavity.
Study of reproductive biology of fishes is very important for better understanding of the annual regeneration of the stock.
4.2 Sexual Characters in Fishes
4.2.1 Sexual characters in fishes
This is grouped into three categories.
1. Monomorphism
No external characters to distinguish the sexes even when they are sexually matured. This includes most of the pelagic
fishes like sardine, seer fish, carangids, etc.
2. Sexual dimorphism
In many species, it is possible to determine the sex from their external body features. This phenomenon of differentiation of
male and female sexes by external characters is called “sexual dimorphism”.

23
a. Permanent dimorphism
b. Temporary dimorphism
In permanent dimorphism, sexes can be distinguished after the onset of sexual maturity including the colour. e.g.: fighter
fish (Betta splendeus).
In temporary dimorphism sexes can be distinguished only during spawning season. During other times, sexes cannot be
distinguished. e.g.: common carp (Cyprinus carpio)
In respect of species which do not exhibit sexual dimorphism, the separation of sexes mostly rely on internal examination
and observation of the gonads.
3. Sexual Polymorphism
In this, both the sexes can be distinguished by more than one character. e.g:Salmon.
Sexual differentiation can be made by observing the gonads only after attaining the maturity. There are two types of
characteristic
1. Primary characters: the characterswhich are actually associated with reproductive process; in case of males –
testis and ducts, in case of female – ovaries and ducts. This can be found out by dissecting the fish.
2. Secondary characters :These are more useful because the fish need not be sacrificed or killed. These characters
occur in mature fishes. The secondary characteristics which have no relation with reproductive process but serve as
additional structures for spawning. e.g: Claspers, Gonopodium, Papillae etc.
However in certain species of finfishes, variations occur in the morphology of fish.
i) Body shape :
Females are heavier and larger in size compared to the males because of the ovaries.
Genital papillae : It is a small tube in cloacal aperture and which distinguishes male from females e.g. darters,lampreys
etc.
Pearl organ (Nuptial tubercles): These are horny short structures seen on the snout, cheek (head region) only in males.
Once spawning is over nuptial tubercles will disappear. e.g.: common carp,minnows.
ii) Fins : Generally fins are larger in males than the females. In some fishes, pectoral fins can be used to distinguish
between males and females. In males, they are rough and grainy in nature (Indian major carps). In some fishes, the caudal
fin can be used to distinguish. e.g.: male sword tail has lower lobe much longer.
iii) Coloration: Most male fishes are brightly coloured and more intense when compared to females. This is common in
most of the aquarium fishes. e.g. parrot fishes.
In Bow fish (Amia sp.), the juvenile develop a coloured circular spot in their caudalfin of both sexes but when they attain
maturity, it disappears in females and it becomes very intense in males.
Accessory sexual characters: It Includes modification of anal fin to an organ called gonopodium (in males) which helps in
the transfer of sperms during maturity. e.g.: mosquito fish, guppies.
Pelvic fins: The pelvic fins are modified into claspers in males and serve as claspers in many elasmobranches.
Female accessory sexualcharacteristic is seen in the form of egg laying tube or ovipositor. e.g.: Asiatic lump sucker.

24
iv) Head characters: In chimaerids, especially the males develop a spiny stout retractile knob like structures called frontal
claspers. This sort of structure is also seen in forehead brooders. In salmons, males develop knob like hook and this is
called as leype, seen at the tip of both the jaws.
v) Size : Deep sea male angler fish parasitic on the body of female. Fishes which have parental care,the secondary sexual
characters are more pronounced. Sexual dimorphism is least pronounced in case of fishes which don’t exhibit parentalcare.
4.3 Maturation and Spawning
4.3.1 Maturation
The term ‘maturation’ can be defined as cyclic, morphological changes which the male and female gonads undergo
to attain full growth and ripeness. “Spawning” refers the release of male and female gametes from the body of fish to the
exterior environment where fertilization takes place. “Breeding” includes all these events along with their prespawning and
spawning phases. The breeding season signifies the time of peak maturity and the period during which spawning occurs in
a population. Breeding behaviour includes complex behaviour pattern involving nest building, pairing, migration, courtship
and shoaling.
4.3.2 Flatfish maturity scale
Females Males
1.
Juvenile
Ovaries small translucent. Tunica lining
silvery or dark in colour.
Juvenile
Testes very small and translucent up to about 1cm long.
2.
Developing virgin / Resting spent
Ovaries up to ½ of length of a full
ovary. Pinkish colour, no yellow or
orange colour visible.
Developing virgin / Resting spent
Testes up to ½ size of full testes grey to white in colour.
3.
Ripening 1
No stage 3 for males
Ripening 1
No stage 3 for males
4.
Ripening 2
Colour yellow to orange, individual
oocytes seen with the naked eye.
Ripening 2
Testes filling but no sperm visible when testes are cut.
No sperm in sperm ducts.
5.
Ripe
Ovaries containing few or many
hydrated eggs, but will not run under
moderate pressure.
Ripe
Testes full but do not run under moderate pressure.
When testes are cut,some sperm is visible. Sperm in
sperm ducts.
6.
Running Running

25
Hydrated eggs extruded on slight
pressure
Testes run on slight pressure
7.
Spent
Ovaries size reduced and flaccid. Some
opaque eggs may occur with slime.
Spent
Testes thin and flabby, little sperm may remain in sperm
ducts.
4.3.3 Maturity stages
The term ‘maturity stages’ is unique but has accepted meaning in Fisheries Biology. It is taken as a measure to observe the
degree of ripeness of the ovaries and testes of a fish and not whether the fish has sexually mature or not. The term first
maturity describes a fish which is spawning for the first time. In other animals, the term maturity is used when an animal
reaches maturity (the ability to reproduce) once again.
To determine the cycle of maturity of gonads, the most common method is to define the stages of sexual maturity and
observe them with large number of samples at weekly intervals. The species to be studied should be brought to the
laboratory. The fish has to be weighed accurately and the total length of each specimen should be recorded. The criteria for
assessment of maturity are the colour of gonads, the size of gonads in relation to body cavity, presence or absence of oil
globule in the ovum, nature of perivitelline space,nature of ova and diameter of the unspawned eggs. The ovaries undergo
maturation process quicker than testes; but the stages can be ascertained more easily in ovary. The ovaries should be
preserved either in formalin or in modified Gilson’s fluid for further studies on ova diameter and fecundity. To know the
distribution pattern of ova in an ovary, ova should be taken from the anterior, middle and posterior regions of few ovaries
during different stages maturity. If the distribution pattern of ova is uniform in all the three regions, then the ova can be
taken in any place irrespective of the regions. If the distribution is not uniform, the ova should be taken from all the three
regions and then it should be pooled.
4.3.4. Intra-ovarian periodicities and frequency of spawning
To study the development of ova, the diameter of ova from immature to fully ripe and spent ovaries should be recorded
using ocular micrometer. Ova-diameter measurements should be taken from 20-25 ovaries in each case.
Table 1. Stages of Maturation
Sex Stage Description of Gonads
Female I. Immature Ovary thin, narrow,cylindrical, occupying less than one-fourth of body
cavity length, pale, translucent.
II.Maturing virgins Ovary thin, narrow,cylindrical, occupying about one-fourth of body
cavity, pale, translucent. Ova translucent, irregularly shaped and slightly
yellow.
III. Maturing Ovary occupies about half of a body cavity, narrow, cylindrical and pale
yellow. Blood capillaries not distinct, ova not clearly visible to the
naked eye; larger ova opaque and smaller ones translucent.
IV. Mature Similar to that in stage III but with numerous blood capillaries. Majority
of ova opaque and visible to the naked eye.
V. Gravid Ovary occupies about three-fourth of body cavity, whitish, with
numerous blood capillaries; ovarian wall thin, ova spherical, opaque
with narrow translucent outer border.

26
VI. Ripe Ovary occupies from three-fourths to entire length of body cavity,
cream-coloured. Ripe ova translucent and with or without distinct oil
globules, already released into the lumen of the ovary, together with
severalmature (opaque) and maturing (translucent) ova.
VII. Spent Completely spawned, ova never seen.
Male I. Immature Testis very small, narrow and thread-like, occupying one-fourth of body
cavity.
II.Maturing virgins Testis slightly more enlarged than in stage 1 but essentially thread-like
and transparent.
III. Maturing Testis has begun to broaden and thicken, turning white in colour
IV. Mature Testis, flat, thick and white; extends to more than half of body cavity
V. Gravid Testis very thick, flat creamy-white; extends to two-thirds of body
cavity, milt oozes freely.
VI. Ripe No changes discernible in testis
VII. Spent Testis has shrunk
4.3.5. Five scale Maturity stage Description
Females I. Immature Ovary small, firm, no eggs visible to the naked
eye
II. Maturing virgin or resting Ovary more extended, firm, small oocytes
visible, giving ovary a grainy appearance
III. Developing Ovary large, starting to swell the body cavity,
colour varies according to species, contains
oocytes oftwo sizes
IV. Gravid Large, filling or swelling the body cavity, when
opened large ova spill out
V. Spent Ovary shrunken, flaccid, contains a fewresidual
eggs and many small ova
Males I. Immature Testis small, translucent, whitish, long, thin
strips lying close to the vertebral column
II. Developing or resting Testis white,flat, convoluted, easily visible to the
naked eye, about ¼ length ofthe body cavity
III. Developed Testis large, white and convoluted, no milt
produced when pressed or cut
IV. Ripe Testis large, opalescent white,drops ofmilt
produced when pressed or cut
V. Spent Testis shrunk, flabby, dirty white in colour

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4.4 Fecundity
4.4.1. Fecundity
The problem of estimating fecundity depends upon severalfactors such as: the absolute numbers of eggs produced the total
or partial spawning nature of the fish and the immature eggs present which will be carried over to the next spawning
season. The methods used in fecundity studies fall into three sections: (1) Random sampling of fish, (2) estimating the
number of eggs and (3) analyzing the results in relation to other parameters. The fixatives and preservatives used are:
1. Formalin and
2. Modified Gilson’s Fluid
It was recommended that Simpson’s modification of Gilson’s fluid should be used in the fecundity estimation
60% alcohol - 100 ml
water - 880 ml
80% nitric acid - 15 ml
glacial acetic acid - 18 ml
mercuric chloride - 20 g
This mixture hardens the eggs and also liberates them from the ovarian tissues. The ovaries should be shaken periodically
in the Gilson’s fluid to help loosen the ovarian tissues and to ensure rapid penetration of the preservative. After 40 hours of
preservation, the eggs can completely be liberated from the tissue by vigorous shaking.
4.4.1.1. Gravimetric method
Gravimetric sampling is based on weighing and counting the eggs. After the eggs have been liberated from the ovarian
tissues, they are thoroughly washed and spread on blotting paper to dry in air. Total number of eggs is then weighed and
random samples of about 500 eggs are counted and weighed. The total number of eggs in an ovary is then calculated from
the equation F = nG/g (where F = Fecundity, n= number of eggs in the subsample, G=total weight of the ovary and, g =
weight of the subsample in the same unit.)
4.4.1.2. Volumetric method
After separation in Gilson’s fluid, the cleaned eggs are put in a measuring cylinder and made up to a known volume with
water. Subsamples are drawn by shaking the container until all the eggs are evenly distributed throughout the water. A
subsample of known volume is again drawn with a pipette, and the number of eggs in the subsample is counted. Then the
fecundity is calculated as follows.
F = nV/v (Where, n = number of eggs in the subsample, V = volume which contain all the total eggs and v = volume of the
subsample).
In practice, it is normally necessary to count eggs from more than one subsample from each fish to get a reliable estimate of
the fecundity.

28
This method is subject to considerable bias because it is very difficult to get all the eggs evenly distributed throughout the
measuring cylinder. Unless great care is taken, the density of the eggs will be more at the bottom of the cylinder than in the
top and middle of the cylinder.
4.4.1.3. Automatic egg counter
Total count of eggs in an ovary can also be made using automatic egg counters. The advantage of using this machine is that
sampling error in any sub-sampling technique is avoided but the only disadvantage is the slowness of this machine.
Fecundity can be estimated by removing the ovaries from females in stages III to V in the case of total spawners. Fecundity
analysis is largely confined to total spawners, because it is difficult to estimate the fecundity of partial spawners. All the
oocytes to be spawned in one spawning cycle might not have been differentiated in the early stages in the case of partial
spawners. In later stages, some developing eggs might be the leftover of already occurred spawning. Adequate estimate of
annual fecundity in such species, depends upon the data on the number of spawning per year, number of eggs shed at each
spawning and the relation between these factors and size & age of the fish.
Sex Ratio
The knowledge of sex composition of catches is of help in understanding whether any differential fishery exists, its
possible bearing of fish stocks and whether sexual congregation takes place during spawning. It indicates the proportion of
males and females in the population. The expected sex ratio is 1:1 in the nature. Variations from this are often observed in
fish because of differential behaviour of sexes, environmental conditions, fishing, etc. The number of male to female ratio
is observed for a minimum period of one year. This data is pooled in two ways – month wise and lengthwise to study the
distribution of sexes according to seasons and size of fish. It also indicates the segregation or aggregation of sexes
according to feeding, breeding or migratory behaviours. The sex ratio is calculated by using the chi-square formula,
x2
= ∑ (O – E)2
/ E to test the homogeneity in distribution of males and females.
Where, O – Observed value; E – Expected value
4.5 Reproductive Strategy
4.5.1. Reproductive and Strategy
This means different methods are adapted by fishes to ensure the success of reproduction. Normally fishes live in a variety
of environmental conditions. Since the fish live in a dynamic changing environment, they have to evolve different method
to ensure success of reproduction. The adaptations are seen in the form of
1. Special anatomical
2. Behavioral
3. Physiological
4. Energetic adaptation
5. Habit

29
All these are collectively referred to reproductive strategies. Whatever may be the strategy the fish adopts, it should ensure
the success of reproduction.
Measure of success of reproduction
The success of reproduction may be measured by different ways.
1. The survival ratio of eggs.
2. The younger ones should be placed in the proximity/close to suitable food material (plenty/ abundant).
3. It should also ensure juvenile to reach the adult stage. Successfulearly development and larval development.
4.5.2. Classification of Reproductive Strategies
It is possible to construct the ecological classification of reproductive strategies (Most of these strategies are manifested in
behavioral pattern and specialized structures. Basically there are 3 categories.
1. Non-guarders of eggs and young ones
2. Guarders of eggs and young ones
3. Bearers
Non-Guarders ofEggs and Young Ones
They do not give protection to eggs and young ones. Once the spawning is over the eggs are not guarded but they are left to
the environment. These non-guarders are divided into 2 groups.
1. Open substrate spawners
2. Brood hiders
4.5.2.1. Open substrate spawners
They simply scatter their eggs in the environment and they do not have specialized reproductive structures. This group is
further divided into two categories.
1. Pelagic spawners (or pelagophils)
2. Benthic spawners.
1. Pelagic Spawners
These are known as pelagophils. They spawn in open waters and this strategy is exhibited by many schooling fish like
sardines, mackerels, and tunas. In addition to pelagic fishes some of the demersal benthic fishes, also release pelagic eggs.
These pelagic eggs are buoyant and are planktonic in nature. Eggs contain oil globule and lot of water content to ensure
floatation.
But these pelagic spawners have some disadvantages.
1. The eggs are exposed to variable wild environmental conditions.
2. These eggs may be eaten by pelagic predators.
3. Low survival rate of spawned eggs and larvae.
2. Benthic spawners
These fishes deposit the eggs on the substratum and eggs are adhesive. They release their eggs on known area and they are
mass spawners and there is no courtship behaviour and also they do not care for eggs and young ones. They lay eggs in
long strings or thick thread. The benthic spawners are broadly classified into 3 categories.

30
a. Spawners on coarse bottom
These fishes deposit their eggs in stone gravel. Again here there are 2 categories.
i. Pelagophils: the eggs are deposited on the rocks. Young ones or embryos are drift in the surface water. e.g:sturgeons
and white fish.
ii. Lithophils: Eggs are deposited on hard substratum but embryos are retained in the bottom. e.g: minnows and perches.
b. Spawners on Plants
Further divided into two categories
i. Phytolithophils: Eggs are deposited on plants, stones and logs of wood (non obligatory). e.g: herrings and minnows.
ii. Phytophils: Eggs are adhesive and are deposited on aquatic plants (obligatory). e.g: common carp.
c. Spawners on sandy bottom (Psammophils)
The eggs are deposited on the sand. e.g: smelts
4.5.2.2. Brood Hiders
They hide their eggs in one way or another, but there is no parental care. This type of strategy is exhibited by benthic
spawner and some fishes bury their eggs. Further divided into five categories.
a) Lithophils:
The eggs are hidden in natural or constructed hiding places. The females build their nest by digging the gravel to form a pit.
e.g: salmon and trout.
b ) Speleophils:
Normally cave spawners exhibit this type of strategy. Eggs are large, adhesive and deposited in the crevices of rocks. This
prevents cannibalism and predation by other fishes.
c) Ostracophils:
These fishes hide their eggs in the shells of living invertebrates, especially in the gill of many invertebrates. Some fishes
deposit the eggs in the gill cavity of molluscan shell for two reasons such as protection and supply of oxygen. e.g: Rhodeus
sericeus. They deposit their eggs in freshwater clam called unio species; snail fish (Cyclopteridae) deposit their eggs in the
gills of crabs.
d) Beach spawners (or Aero- psammophiles)
Fishes incubate their eggs in the beach just above the tidal water level. e.g: puffer fish
e) Xerophils:
There fishes deposit their eggs in mud & sand and eggs are capable of withstanding dry and harsh environmental
conditions. e.g: cyprinodontids

31
4.6 Parental caring fishes
4.6.1. Parental caring fishes
These fishes guard their eggs and young ones. They produce only very few numbers of eggs when compared to non-
guarders and these guarders exhibit territorial behaviour and have elaborate courtship behaviour.
In general, the eggs and larval are guarded by males and protect them from the predators. The males supply plenty of
oxygen to the eggs and this is done through the creation of water current by pushing the water with their fins over the eggs.
Advantages:
1. They produce plenty of oxygen.
2. It removes unfertilized and decayed eggs which may lead to disease problem.
Guarders are divided into 2 types:
1. Substratum spawners
2. Nest spawners
4.6.2. Substratum Spawners
These lay their eggs on substratum. They do not build nests. These substratum spawners are divided into 4 categories
depending on the substratum.
a) Lithophils (Rock spawners): These fishes spawn on flat rocks, males clean the substratum. Courtship and
fertilization takes place on the clean substratum. e.g: Gobies and Puffer fish
b) Phytophils (Plant spawners): these fishes deposit their eggs on plants or release their eggs among the plants.
Sometimes the eggs are sticky. e.g.: cat fishes.
c) Aerophils (Terrestrial spawners)
These fishes deposit their eggs on the underside of the overlying rock or plant (above the water level). They deposit
their eggs by pressing their belly against the rock or plant. Eggs are protected from predators and eggs are ensured with
plenty of oxygen. In tropical areas,oxygen depletion will always be there and dehydration is overcome by spraying or
splashing the water by males over the eggs which always keep the eggs moist. e.g.:Characin spp.
d) Pelagophils
These eggs are released in open water and these eggs are sticky. These adhesive eggs are always found in clusters (in
clumps on clusters) and they are belayed. These eggs are protected by the fishes and the parentalcare is exhibited by
both male and female fish. e.g: climbing perch
4.6.3. Nest Spawners
Before releasing eggs, fishes construct nests. These nests could be any material and any shape i.e., pit or cavity or
depression. Once the nest is built, the female releases the eggs into the nests and the eggs get fertilized and development
takes place inside the nests. The nest is guarded by both the parents. Depending on the kind of material used for building
the nests,there are severalcategories.
1. Lithophils : They use gravel; the nests are guarded by males e.g.: cichlids and minnows
2. Phytophils: They build their nests by using plant material e.g.: Bowfin.
3. Psammophils: They build their nests on sandy bottom. e.g.: cichlosoma spp.

32
4. Aphrophils: They build their nest by bubbles. Bubble nest builder, Siamese fighter (Betta splendens) and some
other fishes like gourami make their nest with the help of froth (foam/scum).
5. Speleophils :These fishes build their nests in natural or constructed cavities or burrows. e.g.: cat fishes.
4.6.4. Burrow Nest Spawners
Males guard the eggs to overcome oxygen depletion, the pelvic fin is developed into feathery thread like structure and they
are highly vascularised and also act as gills. e.g.: south american lung fish.
a. Polyphils: Build their nests with miscellaneous materials. e.g.: arowana.
b. Ariadnophils: Fishes build their nests by using plant materials and these materials are held together by secretion of
kidney. Once the fertilization is over, the males drive away the female from that area and take care of the eggs. e.g.:
stickle backs.
c. Actinariophils: These fishes make use of sea anemones. They usually lay their eggs in and around sea anemones
to avoid predation. e.g.: Amphiprion
4.6.5. Bearers
In case of bearers,fishes carry eggs or embryos. There are two categories.
1. External carriers
2. Internal carriers
4.6.6. External Carriers
3. These fishes carry the fertilized eggs till they hatch. There are different types of external carriers depending upon
the type or mode of carrying.
4. a) Transfer brooders: The eggs are carried by various means and they are deposited elsewhere in a suitable area.
e.g.: cyprinodontids
5. In transfer brooders the eggs are attached to the belly of female fish and these female carry their eggs until they
found suitable area and plants and these eggs are deposited on the plants and guard them till they hatch out.
6. b) Forehead brooders: The unborn offspring (embryos) are placed in a depression on the forehead of the males,
where they keep the young ones in place by threads attached to an overhanging hook like structure. After
spawning, the female transfer the eggs on to the depression or hook like structure on the forehead of males. e.g.:
Kurtidae
7. c) Mouth brooders :These fishes carry their eggs in the mouth till the young ones hatch out. After hatching the
young ones move around their parents, if they find any danger, the young ones jumps into the mouth of the mother.
e.g.: male marine catfish (Ariidae), cichlids – (Usually female carry the embryos, which she picks up quickly after
spawning) and cardinal fishes.
8. d) Skin brooders: These fertilized eggs are attached on to the skin. The female fishes have a layer of spongy skin
on their belly region, once the fertilization is over; the eggs get attached to the spongy skin of the female. This
spongy skin also serves as placenta. e.g.: south american cat fish.
9. e) Pouch brooders :These fishes deposit the eggs in a cutaneous pouch. This is well developed in the case of male
sea horse (Hippocampus). The females deposit the fertilized eggs into the pouches of the males. Even after
hatching the juveniles are seen in the pouch of the male.
4.6.7. Internal Bearers
In these fishes, the fertilization takes place internally. Incubation may take place either internally or externally (to breed or
sit on eggs for hatching). There are 3 major categories. Internal carriers / bearers produce small number of eggs.
a. Ovi-ovoviviparous :Fertilization is internal, incubation is external. No nourishment from the parents. e.g.: sharks
and skates

33
b. Ovoviviparous: Fertilization internal, incubation is also internal without any nutrient supply from the females, but
they get protection (Hatchlings come out from the body of female). e.g.:many sharks and skates and living fossil
fish, Latimeria chalumnae.
c. Viviparous: Fertilization internal, incubation is internal; also they get nutrient supply from females. e.g.: some
sharks – carcharinidae and poeciliidae.
4.7 Developmental Stages of finfishes
4.7.1. Developmental Stages of Finfishes
In broad sense, development is a process by which an organism reaches its adulthood. However, unlike other vertebrates,
the development in fish is continuous. Development starts right from the moment the egg is fertilized. After several stages
of development, the tiny organism attains the maturity (adulthood). The adult organism is capable of producing new life of
its own kind. And after reaching the adulthood also the growth process does not ceases.
The eggs and larvae start life that is completely different from the life of the adults. The moment of hatching is in fact the
beginning of a hazardous period in the life of all aquatic animals including fishes. It then faces the twin problems of
adjusting itself with the physico-chemical factors of the surrounding medium in one hand and to the predators on the other
hand. The development of fish is being discussed here in two heads viz. (i) embryonic development and (ii) larval
development
4.7.1.1. Embryonic development
In a fully ripe egg, a small opening known as micropyle appears in the shell. Through this micropyle, polar body escape
and water from outside enters into it. This causes swelling of the egg. The swelling may be as much as four times of the
original size. Now, a gap called perivitelline space is found in which the embryo is bathed during its development.
Usually, the water mixes with the yolk and makes the egg to become transparent. It may be mentioned here that the
fertilized egg is transparent whereas unfertilized one is opaque. After fertilization, the micropyle is closed and no more
spermatozoa and even water can pass through. Gaseous exchanges,however, can take place through the vitelline
membrane. The environmental conditions particularly the temperature and pH of water has greater influence on the
developing embryo.
Embryonic development begins from the moment the egg is penetrated by a sperm i.e. just after fertilization. The
embryonic development in fishes is basically the same as in other chordates. The fertilized egg first undergoes
segmentation and thus it passes from one-celled to many celled stage. This segmentation is known as cleavage. It is the
process by which the fertilized egg is divided into smaller cells called blastomeres. In both cartilagenous and bony fishes,
the cleavage is incomplete and is confined to the superficial cytoplasmic layer. The deeper yolky portion remains
unchanged (unsegmented). This type of cleavage were only a small disc like part (germinal disc) of the egg which is known
as meroblastic and the disc of cells thus formed on the upper or animal pole is known as the blastoderm. Cleavage
ultimately result in the formation stage which is characterized by the single layered cells (blastomeres) and having
segmentation cavity (called blastocoels) formed under the blastoderm. A large number of free blastomeres form a layer of
cells called the periblast and lie just above the yolk. Actually, the space between the blastoderm and periblast is the
blastocoels. The blastoderm ultimately gives rise to future embryo.
In most bony fishes, gastrulation starts with the presumptive endodermal and mesodermal cells at the posterior end migrate
forwards under the blastoderm, thus forming the hypoblast. The cell of the blastoderm has continued to grow over the
yolk. This process is known as epiboly . The presumptive ectoderm cells grow over and cover the yolk mass from outside,

34
forming a layer of cells called epiblast. Simultaneously periblast also grows and forms an inner covering of the yolk. The
periblast and epiblast enclose the yolk in a yolk sac. Formation of yolk sac signifies the termination of gastrulation. The
embryo proper is now distinctly separated from the yolk sac which can be seen from outside. The embryo is connected with
yolk sac by a yolk stalk. Blood vessels develop in the wall of the yolk sac and as the embryo grows the yolk sac is
gradually reduced in size. This indicates that the yolk sac provides nourishment to the developing embryo.
The characteristic feature of gastrulation in fishes is the formation of primary rudimentary organs which starts in the
anterior part of the embryo. Various organs of the body are formed from the ectoderm, mesoderm and endoderm. The
ectoderm gives rise to the epidermis and its derivatives like brain and spinal cord, the lens of the eye and internal ear.
Similarly, muscles, appendages,axial skeleton, skin, scales etc. develop from mesoderm cells. Endoderm cells make up the
inner lining of the digestive tract and sex cells. Certain endocrine glands such as thyroid and ultimobranchial glands are
also derived from endoderm cells.
The embryonic phase is the interval in which the major organ systems begin to appear. It ends in hatching. However,the
exact state of development into an embryo at the time of hatching not only varies among species but may vary within a
species, depending on environmental conditions. The summary of the embryonic development in Clarias batrachus is
given below .
Stage 1. Fertilized egg.
Stage 2. Two-celled stage (45 min. after fertilization)
Stage 3. Four-celled stage (1 hour)
Stage 4. Eight-celled stage (1hr 20 min.)
Stage 5. Multi-celled stage (2 hrs. 30 min.)
Stage 6. Morula stage (3 hrs. 30 min.)
Stage 7. Formation of germinal ring (5 hours)
Stage 8. Embryo formation (7hrs. 30 min.)
Stage 9. Differentiation of head and tail ends of embryo (10 hours)
Stage 10. Somite differentiate (12 hours)
Stage 11. Formation of optic cups, eight somite stage (14 hrs. 30min.)
Stage 12. 12 somite stage (16 hours)
Stage 13. Kupfer’s vesicle appears (18 hours)
Stage 14. 25 somite stage (19 hours)
Stage 15. Optic cups are visible; Kupfer’s vesicle disappears (20 hours)
Stage 16. Twitching movements starts (20 hrs 30 min.)
Stage 17. Twitching movements more frequent; tail end gets freed (21 hours)
Stage 18. Over 40 somite stage (21 hrs. 30min.)
Stage 19. Twitching movements more vigorous, egg capsule weakens (21hrs. 45min.)
Stage 20. Egg-capsule ruptures (21 hrs. 50min)
Stage 21. Larva hatches out (21hrs. 55min.)
4.7.1.2. Larval development
The larval phase begins once the embryo is free from the egg membrane. The embryo now ceases to be curled up, becomes
increasingly fish like, and continues to rely on its yolk or mother for nutrition (Moyle and Cech, 1988). The duration of this
phase, however, varies widely among species. As soon as the yolk content is absorbed (generally yolk sac is absorbed on
the third day in case of Indian major carps) the larva should develop the ability to capture food organisms. The larva is now
carnivorous taking mainly zooplankton regardless of the species which is herbivorous or carnivorous in later (adult) stage.
A larval fish, while still using its stored yolk, is called either a prelarva or a yolk sac fry. After absorption of the yolk, it is

35
called post larva (advanced fry). Larval development continues until the fry reaches the fingerling stage, when it more or
less resembles the adult. Usually mention may be made that the development in fish larvae does not occur at the same rate
among all the individuals in a population. Biswas and Phukon (1989, 1990, and 1991) in a series of experiment observed
that hatchlings emerging from the eggs of same brooder and same time are not equal in size. This variation in size becomes
more conspicuous when the hatchlings are about two weeks old. It is probable that the sudden increment of growth in a
section of fish spawn is related to genetical factors.
4.8 Fish Eggs
4.8.1. Breeding modes of bony fish
Oviparous
Producing eggs that develop outside the maternal body. e.g.: many bony fishes
Ovo-viviparous
Developing larvae (juveniles) within the maternal body in eggs. e.g.: scorpaenidae, cottidae, hexagrammidae
Viviparous
Developing Juveniles within the parent body by maternal nutrition supply. e.g.:embiotocidae, poeciliidae.
4.8.2. General characteristics of eggs
S.No. Pelagic eggs Demersal eggs
1. Eggs are small in size Eggs are bigger in size
2. Eggs laid singly Eggs are laid in mass
3. contain small yolk content contain more yolk content
4. Prolonged developmental period Developmental period is short
5. Egg membrane is generally thin and smooth Egg membrane is generally thick (with hard
coverings)
6. Fecundity is more Fecundity is less
7. No parental care Mostly with parental care
8. The eggs are transparent
e.g. Sardina pilchardus
Solea solea
Trachurus trachurus
Gadus morhua
Pleuronectes platessa
The eggs are opaque
e.g. Anguilla sp.
Synodus indicus
Clupea harengus

36
4.8.3. Developmental stages of fish eggs
Early stage: Spawning – blastopore closure
Middle stage: blastopore closure – tail bud free
Late stage: tail bud free – hatching
4.8.4. Different types of fish eggs
Pelagic eggs
Isolated eggs (mostly) - The spawned eggs are isolated, not forming any mass.
Agglutinated eggs (Lophiidae) - The spawned eggs are embedded in a gelatinous ribbon/ballon, or agglutinated to each
other forming a mass
Pelagic eggs: The pelagic eggs of most species are small in size, measuring about 0.7 mm to 1.5 mm in diameter. A few
species have larger eggs between 1.6 mm and 2.6 mm in diameter. All pelagic eggs are transparent and are practically
spherical, except for those of anchovies which are oblong (longer than broad). Occasionally eggs are found to be slightly
ovoid.
Pelagic eggs are floating type, smaller in size compared to demersal eggs. These eggs do not have adhesive membrane.
They are buoyant; the buoyancy is maintained by single oil globule. If the oil globule is not there, high percentage of water
is present which helps in floating. During floating stage, dispersion of eggs takes place. The pelagic eggs are subjected to
high mortality mainly due to two factors. i. Predation, ii. Eggs are exposed (carrying) to unfavourable conditions. But this is
compensated by increased fecundity and protracted spawning season.
Demersal eggs
Adhesive eggs (Exocoetidae,Gobiidae) - The spawned eggs adhesive to substratum with adhesive egg membrane or
filaments
Non –adhesive eggs (Salmonidae)
The demersal eggs are generally larger than pelagic eggs which may be laid in masses or singly. These eggs are heavy or
dense. Since they are heavy, they link to the bottom. The eggs are provided with adhesive membrane. They stick on to
other objects with filamentous structure. Normally there is no relation between habitat and type of eggs produced. i.e.
pelagic fishes can produce demersal eggs and demersal fishes can produce pelagic eggs. (Generally most common pelagic
food fish have pelagic eggs)
The pelagic sardine produces pelagic eggs, whereas herring is a pelagic fish but the eggs are demersal. Similarly angler fish
which is a demersal fish but produce pelagic eggs. Deep sea wolf herring is a demersal fish and produces demersal eggs.
4.8.5. Identification keys of isolated pelagic fish eggs

37
Single oil globule
Non-smooth egg membrane (Ilisha elongata)
Smooth egg membrane
Wide perivitelline space (Japanese sardine)
Narrow perivitelline space (Carangidae, Scombridae)
Non-oil globule
Non-smooth egg membrane (Synodontidae, Callionymidae)
Smooth egg membrane
Wide perivitelline space (Anguilliformes)
Narrow perivitelline space (Engraulidae,Chanidae)
Multi-oil globules
Non-smooth egg membrane (Soleidae, Uranoscopidae)
Smooth egg membrane
Wide perivitelline space (Anguilliformes)
Narrow perivitelline space (Cynoglossidae)
Non-smooth: Sculptures in hexagons and projections
4.9 Fish Larvae
4.9.1. Characters used for the identification
 Yolk shape (oval, elliptical)
 Position of oil globule(s) (Single OG: anterior or posterior in yolk; many OGs: scattered or concentrated in yolk)
 Number of myomeres (color, thickness, sculpture, appendage)
 Position of anus (anterior, half body or posterior)
 Fin Fold (origin of position, wide or narrow, sculpture)
 Melanophores (location, form)
4.9.2. Diagnostic features applicable to different groups of fish larvae
1. Short oval body Monacanthidae , Balistidae , Antennaridae
2. Short depressed body Platycephalidae , Pegasidae ,
Dactylopteridae
3. Crest on nape Holcentridae , Carangidae , Leiognathidae ,

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