The Digestive System of the Bony Fish
Ardan Huck July 7, 2002

Digestion is the process of converting food into smaller compounds that can be used by the body.

Food is ingested through the mouth of the fish using the jaws. Most fish have teeth and an immoveable tongue. The food then passes through the pharynx (throat) into the esophagus and into the stomach. Partial digestion takes place here using gastric juices (including acid and enzymes), and then the food proceeds to the intestine for more digestion and absorption into the blood. Some fish have only one size intestine and the difference between a small intestine and a large intestine is indistinguishable. Fish that are predominantly meat eaters usually have a shorter intestine than fish that eat strictly vegetable matter. Waste is then passed out the anus.

Between the stomach and the intestine there is usually a valve called the pyloric valve. Beyond this valve, a duct from the liver and pancreas enter the intestine to secrete digestive enzymes including "pepsin and trypsin" into the food. Pepsin and trypsin are not only secreted into the intestine at this place, but are also formed and secreted into the stomach and intestine all along the stomach and intestine from sub-mucosal cells. The inside of the intestine has many blood vessels to absorb the compounds of the food. The inside of the intestine also contains many "folds of lining" in order to hold more blood vessels and increase the surface area between the blood and the food.

  • "World Book Encyclopedia" by World Book Inc., 1990
  • "Anatomy and Physiology" by Anthony and Thibodeau, 1983
  • "Handbook of Tropical Aquarium Fishes" by Dr. Herbert R. Axelrod and Dr. Leonard P. Schultz, 1990

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