The document discusses the alimentary canal and feeding adaptations in fishes. It describes the different parts of the alimentary canal including the mouth, teeth, buccal cavity, pharynx, esophagus, stomach, intestines, rectum, and digestive glands. It explains how the structure and components of the alimentary canal vary between different fish types, such as carnivorous, herbivorous, and omnivorous, to support their specific diets and feeding behaviors. For example, carnivorous fish tend to have shorter canals and sharper teeth for consuming meat, while herbivorous fish have longer intestines and specialized adaptations like molariform teeth for breaking down plant materials.

1. ALIMENTARY CANAL AND FEEDING
ADAPTATIONS IN FISHES

2. Contents
Introduction
 Alimentary canal in fishes
 Mouth in different fishes
 Teeth in Fishes
 Buccal cavity, pharynx and gill rakers
 Oesophagus
 Stomach
 Pyloric caecae
 Intestine
 Alimentary canal in Lamprey and Sharks
 Alimentary canal in Bony fishes
 Rectum
 Digestive glands
 Digestive enzymes
 Conclusions


3. Introduction
Alimentary canal in fishes
 As in other vertebrates, the alimentary tract can be divided into 1) The anterior part co
nsists of the mouth, buccal cavity, and pharynx.
 2. The posterior part consists of the foregut (esophagus and stomach), midgut or intes
tine, and hindgut or rectum.
 Voluntary striated muscle extends from the buccal cavity into the esophagus, involunt
ary smooth muscle from the posterior portion of the esophagus through the large inte
stine. Barrington (1957), Kapoor et al. (1975), and Fange and Grove (1979) provide det
ailed accounts of the alimentary tracts of fishes.
 In hagfishes and lampreys, the absence of true jaws is correlated with the absence of
a stomach.
 Presumably, the evolution of jaws permitted capture of larger prey, making a storage o
rgan, the stomach, highly advantageous. Both hagfishes and lampreys have a straight i
ntestine, but the surface area of the intestine is increased in the lampreys by the typhl
osole, a fold in the intestinal walls.
 Chondrichthyes increase the surface area of the intestine by means of a spiral valve, a
sort of a spiral staircase inside the intestine

5. .
 Mouth is the anterior opening of alimentary canal .
 Most fish mouth fall into first three general types:
 1 . Superior mouth type: Some species with a superior mouth have an elongated
lower jaw that functions much like a scoop.
 Archers, half-beaks, and hatchetfish and Catla are all examples of species of aquariu
m fish that have a superior mouth.
 2. Terminal mouth type: Most fish that feed on other fish have terminal mouths,
which are often hinged to allow them to accommodate the action of snatching and sw
allowing another fish.
 They may also possess specialized teeth, and in some cases an additional jaw.
 Moray eels are one type of species that have a pharyngeal jaw placed well back in thei
r throat. Most barbs, cichlids, gouramis and tetras have terminal mouths
Mouth in Fishes

6. 3. Inferior or sub terminal mouth type:
Also called a sub-terminal or ventral mouth, the inferior mouth is turned downw
ard. The lower jaw is shorter than the upper jaw, and the jaw will often be pr
otrusible.
Fish with inferior mouths are usually bottom feeders and often possess barbels
that assist in locating food particles. Most members of the catfish family and
Mrigal have inferior jaws, and many of them also have a sucker mouth as w
ell.
The diet of fish with inferior mouths includes algae, invertebrates (such as snail
s), as well as detritus and any food that falls to the bottom.
The mouth of cartilaginous fishes is ventral.e.g. Sharks, Rays and Skates.
4. Protrusible Mouth
5. Sucker mouths are a common feature in fish with inferior mouths. Catfish, s
uch as the popular plecostomus (which literally translates to folded mouth),

7. 6. A greatly elongated snout is another kind of mouth adaptation. This ty
pe of mouth allows the fish to poke into small crevices and holes to find foo
d.
They may also use this mouth to dig through the substrate to reach buried f
ood treasures.
Some surface feeding fish also have an elongated mouth that allows them
to scoop insects and food particles from the surface.
Freshwater species with elongated mouths include the halfbeaks,
7. The beak mouth is an interesting, but less common, mouth variation; it'
s also known as a rostrum. In this design, the mouth consists of two very h
ard pieces that are hinged and come together in a scissor-like fashion. This
allows them to crush hard shells of invertebrates. Pufferfish, both freshwat
er and saltwater species, and Saltwater

9. Outstanding among the obvious oral adaptation for feeding in fishes are the t
eeth.
They are thought to have arisen from scales covering the lips, as represented
in living sharks (squliformies) where the placoid scales of the skin visibly grade
into teeth on the jaws.
In bony fishes (Osteichthyes) Teeth are of three kinds, based on where they
are found Jaw, Mouth and Pharyngeal.
Jaw TeethJaw teeth are variously those on the maxillary and premaxillary bo
nes above and on the dentaries below.
In the roof of the oral cavity teeth are variously borne by the median vomer an
d by the palatine and ectopterygoid bones on each side. In the floor of the mout
h the tongue often has teeth on it.
Teeth

10.  Pharyngeal teeth occur as pads on various gill arch eolements in many species. In
the carps (cyprinedae) and suckers (cjcatastromidae) the only teeth are those in deep
in the pharynx (gut, mouth and eoesophagous) that develoed modification of lower el
ements after last gill arch, in clarius and labeo the teeth are modified for grasping, te
aring, grinding and razor like cutting teeth have developed in predacious fishes.
 Kinds of jaw teeth
Based on their form major kinds of Jaw teeth are
1) Cardiform 2) Villiform 3) Canine 4) Incisor and 5) Molariform.
1) Cardiform Teeth Cardiform teeth are numerous, shrotfine and pointed such de
ntition with variations is found in many fishes that have multiple rowed teeth. For ex
ample American catfish (Ictaluridae) perches (percidae) and many sea bases (serrani
dae)

11.  2) Villiform teeth Villiform teeth are more or less elongated cardiform teeth. For example : Nee
dlefishes (Belonidae) and Lion fishes as (Pterois).
3) Canine teeth Canines are dog tooth like or fange like (long pointed tooth) they are elongated a
nd subconical, straight or curved and are adapted for piercing and hodling for example walleyes (Al
ska pollock) (Stizostediosn). In certain fishes such as moreys (muraenidae) the canines are hinged (
the hook) yield ot backward pressure but lock when moved forward and adaptation to retain living
moving prey inside the mouth.
 4) Incisors teeth
Incisors are sharp edged cutting teeth. In some fishes incisors fuse together in cutting beak as in pa
rrot fishes (scaridae).
 5) Molariform teeth
Molariform teeth are for crushing and grinding thus flat with prodruding denticles on the surface.
These teeth are found in bottom dwelling fishes like skates and rays and some sciaenidae (drums).

12. Diversity in dentition in Bony fishes
 With in a single group the diversity of dentition on identical bones may vary largely.
For example In carps and minnows (cyprinidae) the pharyngeal teeth range from sh
arp in carnivores such as in semotilus to molariform in the common carp (Cyprinus
carpio).
In general teeth are absent in plankton feeders and in some of the more generalize
d omnivore.
 They are present in increasing numbers of bones in more and more relative to its pr
edatory behaviors.
 The premaxillary bones are toothed when jaw bones have little or no teeth. This is t
rue for many soft rayed species such as bowfin (Amia) the gars (lepisosteus) the sal
mons and trouts (Salmonidae).
 The maxillae are typically toothed in those soft rayed fishes as that carry premaxilla
ry teeth. However tooth less in otherwise tooth – bearing spiny rayed fishes.

13. Teeth adapted for crushi
ng hard shell of mollusk
s & crustaceans

14. Four types of shark teeth include:
 Dense flattened: Nurse sharks and angel sharks use their dense flattened teeth to crush
crustaceans and mollusks.
 Needle-like: Blue sharks and bulls sharks use their needle-sharp teeth to grab and eat s
mall- to medium-sized fish such as flounder, stingrays, and even smaller sharks.
 Pointed lower with triangular upper: These razor-sharp teeth are a famous trait of the G
reat White shark, which feeds on large mammals and fish like dolphins, sea lions, other s
harks, and small whales.
 Non-functional: Pretty much useless, these teeth belong to plankton feeders such as the
basking shark and whale shark that simply suck food into their mouths without chewing.

15. BUCCAL CAVITY, PHARYNX
& GILL RACKERS
The buccal cavity and pharynx are not clearly marked off from each oth
er.
 A number of perforations of gill slits are located on each side of the ph
aryngeal wall.
 Primary function of the gill rakers is to protect gill filaments from injury
and to assist the fishes in the process of ingestion .


16. OMNIVOROUS
In the omnivorous fishes
like Puntius sarana,gill ra
kers are short and
stumpy.
HERBIVOROUS:
Like Labeo rohita,Cirrhina marigala,
gill rakers form a broad sieve like st
ructure across the gill slits for filteri
ng the water in order to retain the f
ood in the bucco-pharynx

17. Carnivorous Fishes : Gill rakers are normally long, ha
rd and teeth like forming rasping organs as in Wallago attu, Mystu
s seenghala, Channa striatus.

18. Oesophagus
The pharynx opens behind into the oesophagus which have large nu
mber of mucus secreting cells which are scattered in the mucosa.
Taste buds are also present e.g. Labeo rohita, Cyprinus carpio, Catla
catla
 Short & narrow tube in case of herbivorous and omnivorous fishes e.
g. Labeo rohita, Puntius sarana, Cyprinus carpio etc
Large & distensible tube in case of carnivores and predatory fishes (
e.g. Wallago attu, Heteropneustes fossilis etc.

19.  Stomach
ANTERIOR – CARDIAC STOMACH
STOMACH
POSTERIOR – PYLORIC STOMACH
•Stomach acquire different shapes according to the availability
of space in the body cavities of different fishes.
 A true stomach is present in the carnivorous and predatory fishes e.g
. Channa striatus, Mystus seenghala etc .
 intestinal bulb (Stomachless Fishes ):
 All the fishes do not possess a true stomach as it is almost absent in
various herbivorous fishes like Labeo rohita,Catla catla etc.
 About 15% of teleosts, including cyprinids, have no stomach and no region of lo
w pH or pre-digestion. Anterior portion of intestine has some storage function, i
ntestine in these species is usually very long compared to, say, a trout (Rombo
ut, et al. 2011).
 In such fishes, the anterior part of the intestine is swollen to form a s
ac like structure called intestinal bulb.

20. Carnivorous fishes:• Stomach is generally sac-like a
nd thick walled in Carnivorous an
d predatory fishes.
Omnivorous fishes:
 Stomach of omnivorous fishes is also sac like .e.g. Puntius
sophore,Cyprinus carpio etc.
 In some fishes like Hilsa hilsa,Gudusia chapra, stomach is red
uced in size but is greatly thickened to become gizzard like for
trituration of food

21. Pyloric caeca
•Anterior part of the intestine
give rise to a number of finger
-like outgrowths called
pyloric or intestinal caeca.
• Pyloric caeca serve as access
ory food reservoirs .
•Histologically, intestinal caeca
resembles the intestine and pr
obably serve to enhance the a
bsorptive area.

22. Intestine
• The part of alimentary canal that follows the stomach is called inte
stine and is divided into two parts:
1.Anterior part : small intestine
2.Posterior part : large intestine
 The small intestine just behind the stomach receives ducts from th
e liver and pancreas is called as duodenum while rest part is called il
eum .
 There is no clear cut demarcation between the small intestine and
large intestine .
 The length of the intestine depends upon the feeding habit of the fi
sh.

23. Carnivorous fishes : It is shortened in carnivore
s such as in Wallogo attu, Mystus seenghala because flesh
can be digested more readily than the plant based food stu
ff.

24. Herbivorous fishes:
 Intestine is often elongated and arranged in many folds in case of herb
ivorous fishes.
 Longer intestines are of great advantage to herbivorous fishes as they r
etain food for long period of time to ensure digestion.

25. Omnivorous fishes:
 Intermediate length of the gut is found in case
of omnivorous fishes e.g. Puntius sophore etc.
 The intestinal bulb of Labeo rohita is about 25c
m,the small intestine about 8m and the large inte
stine about a meter in length.

26. Alimentary canal in Lamprey and Shark

27. Alimentary
canal
in
Bony
Fishes

28. Rectum
•It is not usually distinguishable externally but an ileo-r
ecta valve is present in few species of fish to demarcate
it from the intestine e.g. Tetradon
•Histologically ,the mucosal folds of the rectum differ fr
om the intestine in being shorter and broader, possess
a large number of mucus secreting cells produce copio
us mucus to lubricate waste food and aid in easy defec
ation

29. Digestive glands
 The digestive system consists of alimentary canal and its associated glands. The diges
tive tube also contains numerous intramural glands which provide the tube by lubrica
ting mucus, enzymes, water, etc.
 The extramural glands are liver, pancreas and gall bladder (Fig. 4.1a, b). The liver is pr
esent in all fishes.
 The pancreas which is exocrine and endocrine organ, may be a discrete organ or it m
ay be diffused in the liver or in the alimentary canal.
 In sharks and rays (Elasmobranchii) pancreas is relatively compact and usually well d
eveloped as a separate organ, often two lobed, but in teleosts, the pancreas is diffus
ed in the liver to form hepatopancreas.
 It is also diffused in the alimentary canal in a few fishes. It is also present in the mese
nteric membranes surrounding the intestine and liver.
 The gall bladder is vestigeal in deep sea fishes but it is prominent in other fishes.
 While passing through the alimentary canal, the food is broken down physically and c
hemically and ultimately solubilized so that degraded products can be absorbed. The
absorption occurs chiefly through the wall of intestine.

31. Two main digestive glands in Fish :
1 . Pancreas: pancreas is a diffuse gland, but is well developed around the
blood vessels between the lobes of the liver.
Pancreas has two digestive functions:
1.Source of exocrine secretion into the intestine.
2.Endocrine secretion of the hormones insulin and glucagon .
2.Liver:
• Liver is a bilobed gland usually yellowish brown in color.
• The liver in fish produces bile
which is stored in the gall bladder.
• Key storage of food energy
in the form of glycogen.

32. Conclusions
Various structures have been modified according to the natu
re of the food and feeding habits of the fish.
 Position and shape of the mouth.
 Dentition.
 Lips may become cornified as in case of Labeo, granular
or papillated.
 Taste buds and mucus secreting cells .
 Structure of pharynx and gill rakers have also undergo m
odifications according to the feeding habit of the fish.
 Relative length of the gut (RLG).
Continue….

33. Conclusions
The structure of the alimentary canal varies in d
ifferent species of fishes and is generally adapted
in relation to the food and feeding habit.
The variations are seen in the position of the mo
uth, architecture of the buccopharynx, relative len
gth of the gut, presence or absence of the stomac
h and pyloric caeca.
Thanks.

34. Textbook of fish biology and fisheries by S.S. Khanna & H.R. Si
ngh (2005)
Ichthyology by Lagler et al 1977
https://fr.slideshare.net/asimhaq1/alimentary-canal-and-feeding-a
daptations-in-fishes-by-nusrit