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A group of organs that break down food and liquids into nutrients that the body can use is known as Digestive system.
Digestive system is divided into 2 parts i. e.
Digestive system in fish:-
★ Alimentary canal
The major parts of the alimentary canal are buccal cavity, pharynx, oesophagus, stomach, intestine and cloaca.
Buccal cavity:
– The mouth present on the ventral side of the head is small crescentic or semi oval and bounded by jaws.
– The lower jaw is movable, limbs are absent, jaw is covered by spiny skin.
– Teeth are sharp, homodont, backwardly directed polyphyodont and mainly used for grasping of prey.
– Pallet is absent, the skull forms the root of the buccal cavity.
Tongue:
– Tongue is small, non muscular, non glandular, non protrusible attached at the base, lacking test buds, not used in food capture.
Pharynx:
– Buccal cavity marges insensibly into a large posterior pharynx.
– It is a soft wide tube with thick, muscular wall, longitudinal mucous folds and opening into the cardiac stomach with a sphincter or Esophageal valve.
Stomach:
– It is large, muscular, U-shaped, or S-shaped, divided into a long broad proximal cardiac stomach and short narrow distal pyloric stomach.
– Junction of the two marked by a blind sac and a sphincter valve.
– Longitudinal mucous folds well developed in the cardiac part.
– The pyloric stomach opens through the pyloric valve into the bursa entiana
Small intestine:
– There is no external differentiation between duodenum and ileum.
– Mucous lining of intestine folded into spiral valve and villis are absent.
– Sacculus rotundus is absent.
Large intestine:
– The last part of the intestine forms a short rectum of narrow diameter opening into the cloaca.
– Caecum and vermiform appendix absent.
– A tubular rectal gland of unknown function opens dorsally into rectum.
Cloaca:
– The rectum opens behind into a simple cloaca through anus guarded by the anal sphincter.
– Bursa fabricius absent.
– Cloaca opens by a mid ventral longitudinal slit between pelvic fins.
★ Digestive glands in fish
– Mucus gland and salivary glands are absent.
– Gastric glands are present in the stomach.
– Gastric juice contains pepsin and HCl.
– The other major glands are liver and pancreas.
Pancreas:
– A compact, whitish and bilobed gland found between cardiac and pyloric stomach.
– Pancreatic duct opens as a single independent duct into the proximal end of the intestine.
Liver:
– It is a massive, yellowish, bilobed gland in the abdominal cavity.
– The gallbladder is Y-shaped thick walled and attached to the right liver lobe.
– A single bile duct opens independently into the beginning of the intestine.
Fig . Digestive system of fish.
References:
- Kapoor, B. G., Smith, H., & Verighina, I. (1975). The alimentary canal and digestion in teleosts. Advances in Marine Biology, 13, 109-239.
- Wilson, J. M., & Castro, L. F. (2011). Morphological and functional diversity of the gastrointestinal tract in fishes. Fish Physiology, 30, 1-55.
- Ferraris, R. P., & Ahearn, G. A. (1984). The intestinal nutrient transport of teleost fishes. Comparative Biochemistry and Physiology Part A: Physiology, 77(3), 397-413.
- Horn, M. H. (1989). Biological processes regulating food intake and digestion in herbivorous fishes. Reviews in Aquatic Sciences, 1(1), 91-116.
- Jobling, M. (2012). Fish Bioenergetics. Springer Science & Business Media.
- Evans, D. H., Claiborne, J. B., & Currie, S. (2013). The physiology of fishes (4th ed.). CRC Press.
