Feeding types- filter feeders, carnivores,
omnivores and their trophic levels.
Ontogenic changes in feeding- Forage
theory- Mismatch hypothesis of
Presented by- Parul
FRM Dpt. (2020FS06M)
Categories of food
Food available in the nature can be classified as
• Plankton : Plankton is microscopic organisms with little or
no power of locomotion. They drift at the mercy of water
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.
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
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 fecal matter.
Natural feed is found
naturally in the pond .It
may include detritus,
snails, aquatic plants
and fish. Their
organic depend on water
Supplementary feeds are
feeds regularly distributed
to the fish in the pond.
They usually consist of
cheap material locally
available such as
terrestrial plants, kitchen
wastes or agricultural by
Complete feeds may also be
regularly distributed. They
are made from a mixture of
ingredients to provide all
the nutrients necessary for
the fish to grow well. They
must be made in a form
which the fish find easy to
eat and digest. These feeds
are quite difficult to make
on the farm and are usually
quite expensive to buy
Filter feeders are a sub group of suspension feeding
animals that feed by streing suspended matter and
food particles from water, typically by passing the
water over a specialized filtering structure.
Some animal that used this method of feeding are
clams, krill, sponges, Balvn whales and many fish.
Filter feeders can play on important role in
clarification water and are therefore ecosystem.
They are also important in bioaccumulation and as a
result as indicator organisms.
Feeding on both plant and
An omnivore will eat a variety
of meat and vegetable matter.
Their teeth and digestive tract
possess same of the traits of
both the carnivore and
Although omnivores can and
will eat vegetable matter, they
cannot digest some type
grains and plants.
Ex- Etroplus suratensis,
Cyprinus carpio, Tor
They are meat eating and
generally requiring live
They have large mouth with
sharp pointed teeth.
Carnivorous has a short
intestinal tract and a relatively
large stomach designed to hold
on entire fish.
snail/clam, black crab.
Feeding on fish other than
its own species. But
generally they preyupon
small fishes of other
species rather than their
Feeding on the young
ones of the same
Feeding mainly in insect
and crustacean larvae /fish
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
1. Euryphagic : Fishes feeding on a mixed diet with
no preference to any certain type.
2. Stenophagic : Fishes feeding on limited kinds of
3. Monophagic : Fishes consuming only one kind of
Food webs largely define
ecosystem, and the tropic levels
define the position of
organisms within the webs.
But there tropic levels are not
always simple integers, because
organisms often feed at more
than one tropic level.
The feeding habits of a juvenile
animal, and consequently its
trophic level, can change as it
1)In plants and detritus
2)In herbivores and
In secondary consumers.
At the base of the food
chain lies the primary
Primary producers are
principally green plant
and certain bacteria.
Daniel Pauly sets the values of tropic levels to one
They convert solar energy into organic
Above the primary producers are the
consumers who ingest live plants or
the prey of other.
Decomposers, such as bacteria, molds
and fungi make use of energy stored in
already dead plant and animal tissues.
Fungi, like mushroom, absorb
nutrients from the organisms by
secreting enzymes to break up the
chemical compounds that make up
dead plants and animals.
Trophic levels can be represented by
numbers, starting at level 1 with plants.
Further trophic levels are numbered
subsequently according to how far the
organism is along the food chain.
Level 1: Plants and algae make their own food and are called primary
Level 2: Herbivores eat plants and are called primary consumers.
Level 3: Carnivores which eat herbivores are called secondary consumers.
Level4: Carnivores which eat other carnivores are called tertiary
Level5: Apex predators which have no predators are at the top of the food.
Three different food chains
where the energy passed
from smaller to large
Parasite chain- where the
energy is passed from large
to small organisms.
Saprophyte chain- where
the energy is passed from
dead organic matter to
Food chain and food web
Food is passed through
all parts of these chains
before decomposed to
inorganic nutrients by
bacteria and fungi. The
within a community or
ecosystem forms many
food chain which
interconnect or cross
each other in a complex
pattern is referred as
Ontogenic change in feeding
Ontogenic change in feeding refer to the change in organism
resource use pattern as it increases in size from birth or
hatchling to its maximum.
Besides the body size, many other important factors like
predation risk and susceptibility to physical factors also affect
the feeding behaviour of the organism.
So many species undergo exterisive ontogenic shifts in food
and habitat use based on their resource utilizing abilities and
As most fish species continue to grow in their
The substantial increase in body size that a fish achieves
during ontogeny has an implication for species
interaction(werner & gilliam, 1984)
The diets of most fishes change with growth, but the timing of
there change varies from species to species and is often
associated with change in lifestyles or habitats(blaber,2000)
The ultimate objective of ontogenetic change is to maximize
energy intake, enhance growth rate and minimize the risk of
The rapid growth of fish is obvious in the first year, and as it
grows it is capable of handling large size foods.
This is also the period when their diets change rapidly.
Ontogenic shifts are not only for the species that
metamorphose, but also approximated in many groups where
morphology simply change allometrically with growth.
Yellow perch(Perca flavescens), small mouth bass
(Micropterus dolomieui) and largemouth bass (M.
Salmoides) shifts their diet from small entomostracans to
insects and fish in later stage(clay, 1974)
Some of the major factores affecting
Ontogenic change in feeding in fishes
OFT is a behavioral ecology modal
that helps predict how an fish
behaves when searching for food.
Although obtaining food provide
the fish with energy, searching for
and capturing the food require
both energy and time.
To maximize fitness, an fish adopts
a foraging strategy that provides
the most benefit for the best lowest
cost, maximizing the net energy
OFT helps predict the best strategy
that an fish can use to achieve this
Optimal forage theory(OFT)
Mismatch hypothesis of Cushing
The hypothesis focused on the timing, as a function of
the blooms of primary producers.
Blooms of phytoplankton directly influence the increased
population size of zooplankton, as the phytoplankton are
the primary food source for zooplankton.
Most pelagic fish, in their larval stages, feed directly
upon the phytoplankton and zooplankton.
So as logic follows, large population of phytoplankton
will support large populations of zooplankton, and the
presence of both will sustain larval fishing.
As Cushing noticed, however, there are climatic
influences where temperature anomalies will inhibit
phytoplankton blooms, or impact the range of the bloom.
https.//en wikipedia.org wiki Filter feeder.
http ecourse online jasti.res in mod'pa/view php?id
Dr. P.U. Zacharia Trophic levels and Food chain
Head, Demersal Fisheries Division CMFRI. Kochi
326232367 Ontogenic Changes Feeding in Fishes.