Digestive System of Fish & Shellfish

Digestive system of Fish & Shellfish

Anatomy – Organs

Digestive Physiology /FNB 30

Digestive system of fish

GastricAgastric

a.Rainbow Troutb. Channel Catfishc. Common Carpd. Milk Fish


Alimentary canal- PartsKofdarm- mouth, buccal cavity&

pharynxRumfdarm- Remaining Part of

the canal


Mouth & Bucco-pharynx

Predigestive processing of foodSelectionSeizureOrientation

Gill Rakers Pharyngeal teeth Tongue-Retention of prey,sensory organ No enzymatic activity No salivary gland


Oesophagus (Gullet) Lined by striated muscles

Contracts voluntarilyRegurgitation of food

Osmoregulatory function during catadromous migration

Cardiac sphincter at the junction between oesophagus & stomach

Acts as a well lubricating transit tube Oesophagial sacs & glands- trituration & mucus

Production Few club cells, even taste buds may be present


Stomach

Never present in larval stage, appears around the time of metamorphosis

Y or J shaped separated from intestine by sphincter/ valve

Endodermic epithelium with numerous villi – digestive proenzymes, HCl

Mucus secretory cells- only in distal part Stomach

Anterior region-gastric glands more commonPyloric region- Pyloric caecae & gizzard.

pH of the stomach is 2.0-3.0 reaches upto 5.0 in marine fish


Intestine• Length varies with respect to their food habit.• May have 3 regions-

• Duodenum-(large no.of chylomicrons in epithelial cells.)

• Jejunum -(Pinocytic activity and cells containing absorbed granules)

• Ileum• The lumen is linedby columnar epitheliunm with

brush border of microvilli• Goblet cells produce zymogen and mucus.• Rodlet cells/pear shaped cells- function controversial.• pH of the intestine is usually 7.0-11.0


Rectum Presence of rectum in the gut varies with

species. Most distal part, thick muscular coat and

increased no of goblet cells. Peritrophic membrane- absorption of water

from faeces. The no. of goblet cells is known to change

with feeding habit and starvation.


Pyloric Caecae

Present near the proximal part of intestine.

These are finger like blind ending diverticula.

Number varies with species to species.Have well developed muscularis with

circular muscles.Functions:

Suplementing the digestive function of stomach.Increasing the intestinal surface area.Endocrine gland(precursor of pancreas.)Absorption of amino acid. Carbohydrate, Lipid)


Digestive System of Shellfish-Crustaceans

The system divided into six parts:MouthOesophagusStomachHepatopancreasMidgutHindgut


Mouth• Surrounded by :

• Maxillae• Maxillulae• Mandible• Maxillipedes

• Upper lip: Labrum- thick fleshy• Lower lip: Labium- thin comparatively• Functions:

• Chemoreception• Prey capture• Manipulation


Oesophagus

Walls of the Oesophagus made of chitino-protein complex.

The lumen is lined by chitin.The chitin sheds out during each

moult.


StomachTwo parts:I. Cardiac chamber

I. Ridge with row of hard pointed projections called OSSICLES

II. Ossicles and calcarious teeth- forms Gastric mill.

Gastric mill.- breaking, grinding and manipulation.

II. Pyloric groove:I. Bears folds, spines, bristlesII. Allows finest particles of food bolus

to pass.


HepatopancreasMassive organ- made up of two

symmetrical lobes.Represents 2-6% of body mass.Formed of 100s of blind ending tubules

opening into pyloric chamber of stomach.

In larvae, hepatopancreas becomes differentiated in the form of diverticula from each side of the stomach.

This is the store house of most of the enzymes.


MidgutExtend from pyloric to rectum.Surface area increased by long

caecae and covered by well developed “Microvilli”

Mucus mass as pellicle of chitin forms a cylinder which envelops the faecal mass.


Hindgut

The distal part of digestive tract opens into anus.

Very short and straight. Waste particles are swept out

through this.Peritrophic membrane- water

absorption.


Role of Digestive Organs.


Organ/site Fluid/Enzy. Role/func.

Stomach1. Gastric secretion2. Gastric Glands

HClReduces gut pH and allows pepsinogen to act

Zymogens, PepsinogenPepsin

Proteolytic enzyme

Lipase Lipolytic

Chitinase Chitinolytic

PancreasEnzymes

Activation, zymogens

HCO3 – Neutralise HCl

ProteasesProtein breakdown

Lipase Lipid breakdown

Chitinase Chitin digestion

(Role Contd….)


Organ/site Fluid/Enzy. Role/func.

Liver Bile saltsBile pigmentsAnionsCholesterols

Make the intestinal medium alkaline,Emulsification

Intestine Aminopeptidase

Splits nucleosides

Polynucleotidase

Splits nucleic acid

LecithinaseSplits phospho lipids

Carbohydrate digesting enzymes

Carbohydrate digestion

Digestive System of Fish & Shellfish

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