The document provides an overview of the alimentary canal in fishes. It describes the various parts of the canal including the mouth, teeth, buccal cavity, pharynx, esophagus, stomach, intestines, rectum, and digestive glands. It explains how these structures vary between different types of fish depending on their diet, such as carnivorous fish having shorter intestines and herbivorous fish having longer intestines. The adaptations allow for efficient ingestion and digestion of food sources based on a fish's feeding habits.

1. 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


2. Introduction
Alimentary canal in fishes
 As in other vertebrates, the alimentary tract can be divided into 1) The anterior
part consists of the mouth, buccal cavity, and pharynx.
 2. The posterior part consists of the foregut (esophagus and stomach), midgut
or intestine, and hindgut or rectum.
 Voluntary striated muscle extends from the buccal cavity into the esophagus,
involuntary smooth muscle from the posterior portion of the esophagus
through the large intestine. 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 organ, the stomach, highly advantageous. Both hagfishes and lampreys
have a straight intestine, but the surface area of the intestine is increased in the
lampreys by the typhlosole, 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

4. .
 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 hatchet fish and Catla are all examples of species of
aquarium 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 swallowing 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 their throat. Most barbs, cichlids, gouramis and tetras have terminal mouths
Mouth in Fishes

5. 3. Inferior or sub terminal mouth type:
Also called a sub-terminal or ventral mouth, the inferior mouth is turned
downward. The lower jaw is shorter than the upper jaw, and the jaw will often
be protrusible.
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 well.
The diet of fish with inferior mouths includes algae, invertebrates (such as
snails), 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,
such as the popular plecostomus (which literally translates to folded mouth),
use a sucker mouth to rasp algae off driftwood or rocks.

6. 6. A greatly elongated snout is another kind of mouth adaptation. This
type of mouth allows the fish to poke into small crevices and holes to find
food.
They may also use this mouth to dig through the substrate to reach buried
food 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
hard pieces that are hinged and come together in a scissor-like fashion.
This allows them to crush hard shells of invertebrates. Pufferfish, both
freshwater and saltwater species, and Saltwater

8. Outstanding among the obvious oral adaptation for feeding in fishes are the
teeth.
In bony fishes (Osteichthyes) Teeth are of three kinds, based on where they
are found Jaw, Mouth and Pharyngeal.
Jaw Teeth Jaw teeth are variously those on the maxillary and premaxillary
bones above and on the dentaries below.
In the roof of the oral cavity teeth are variously borne by the median vomer
and by the palatine and ectopterygoid bones on each side. In the floor of the
mouth the tongue often has teeth on it.
Teeth

9.  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 oesophagus) that developed modification of lower
elements after last gill arch, in clarius and labeo the teeth are modified for grasping,
tearing, 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
dentition with variations is found in many fishes that have multiple rowed teeth. For
example American catfish (Ictaluridae) perches (percidae) and many sea bases
(serranidae)

10.  2) Villiform teeth Villiform teeth are more or less elongated cardiform teeth. For example :
Needlefishes (Belonidae) and Lion fishes as (Pterois).
3) Canine teeth Canines are dog tooth like or fange like (long pointed tooth) they are elongated and
subconical, straight or curved and are adapted for piercing and hodling for example walleyes (Alska
pollock) (Stizostediosn). In certain fishes such as moreys (muraenidae) the canines are hinged (the
hook) yield a 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 parrot
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).

11. Teeth adapted for
crushing hard shell of
mollusks & crustaceans

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

13. OMNIVOROUS
In the omnivorous fishes
like Puntius sarana,gill
rakers are short and
stumpy.
HERBIVOROUS:
Like Labeo rohita,Cirrhina
marigala,gill rakers form a broad
sieve like structure across the gill
slits for filtering the water in order
to retain the food in the bucco-
pharynx

14. Carnivorous Fishes : Gill rakers are normally long,
hard and teeth like forming rasping organs as in Wallago attu,
Mystus seenghala, Channa striatus.

15. Oesophagus
The pharynx opens behind into the oesophagus which have large
number 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.

16.  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
low pH or pre-digestion. Anterior portion of intestine has some storage function,
intestine in these species is usually very long compared to, say, a
trout (Rombout, et al. 2011).
 In such fishes, the anterior part of the intestine is swollen to form a
sac like structure called intestinal bulb.

17. Carnivorous fishes:• Stomach is generally sac-like
and thick walled in Carnivorous
and 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
reduced in size but is greatly thickened to become gizzard like
for trituration of food

18. 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
accessory food reservoirs .
•Histologically, intestinal caeca
resembles the intestine and
probably serve to enhance the
absorptive area.

19. Intestine
• The part of alimentary canal that follows the stomach is called
intestine 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
the liver and pancreas is called as duodenum while rest part is called
ileum .
 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
fish.

20. Carnivorous fishes : It is shortened in
carnivores such as in Wallogo attu, Mystus seenghala
because flesh can be digested more readily than the plant
based food stuff.

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

22. 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
25cm,the small intestine about 8m and the large
intestine about a meter in length.

23. Alimentary canal in Lamprey and Shark

24. Alimentary
canal
in
Bony
Fishes

25. Rectum
•It is not usually distinguishable externally but an ileo-
recta 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
from the intestine in being shorter and broader, possess
a large number of mucus secreting cells produce
copious mucus to lubricate waste food and aid in easy
defecation

26. Digestive glands
 The digestive system consists of alimentary canal and its associated glands.
The digestive tube also contains numerous intramural glands which provide
the tube by lubricating mucus, enzymes, water, etc.
 The extramural glands are liver, pancreas and gall bladder (Fig. 4.1a, b). The
liver is present in all fishes.
 The pancreas which is exocrine and endocrine organ, may be a discrete organ
or it may be diffused in the liver or in the alimentary canal.
 In sharks and rays (Elasmobranchii) pancreas is relatively compact and
usually well developed as a separate organ, often two lobed, but in teleosts,
the pancreas is diffused in the liver to form hepatopancreas.
 It is also diffused in the alimentary canal in a few fishes. It is also present in
the mesenteric 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 chemically and ultimately solubilized so that degraded
products can be absorbed. The absorption occurs chiefly through the wall of
intestine.

28. 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.

29. Conclusions
Various structures have been modified according to the
nature 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
modifications according to the feeding habit of the fish.
 Relative length of the gut (RLG).
Continue….

30. Conclusions
The structure of the alimentary canal varies in
different species of fishes and is generally
adapted in relation to the food and feeding habit.
The variations are seen in the position of the
mouth, architecture of the buccopharynx, relative
length of the gut, presence or absence of the
stomach and pyloric caeca.
Thanks.