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
Digestive Physiology /FNB 30
Alimentary canal- PartsKofdarm- mouth, buccal cavity&
pharynxRumfdarm- Remaining Part of
the canal
Digestive Physiology /FNB 30
Mouth & Bucco-pharynx
Predigestive processing of foodSelectionSeizureOrientation
Gill Rakers Pharyngeal teeth Tongue-Retention of prey,sensory organ No enzymatic activity No salivary gland
Digestive Physiology /FNB 30
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
Digestive Physiology /FNB 30
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
Digestive Physiology /FNB 30
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
Digestive Physiology /FNB 30
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.
Digestive Physiology /FNB 30
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 Physiology /FNB 30
Digestive System of Shellfish-Crustaceans
The system divided into six parts:MouthOesophagusStomachHepatopancreasMidgutHindgut
Digestive Physiology /FNB 30
Mouth• Surrounded by :
• Maxillae• Maxillulae• Mandible• Maxillipedes
• Upper lip: Labrum- thick fleshy• Lower lip: Labium- thin comparatively• Functions:
• Chemoreception• Prey capture• Manipulation
Digestive Physiology /FNB 30
Oesophagus
Walls of the Oesophagus made of chitino-protein complex.
The lumen is lined by chitin.The chitin sheds out during each
moult.
Digestive Physiology /FNB 30
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.
Digestive Physiology /FNB 30
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.
Digestive Physiology /FNB 30
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.
Digestive Physiology /FNB 30
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.
Digestive Physiology /FNB 30
Role of Digestive Organs.
Digestive Physiology /FNB 30
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….)
Digestive Physiology /FNB 30
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