Physiology of Finfish and Shellfish (2+1)

4.3.1.1 Digestion of proteins

The fishes, which possess stomach are generally carnivorous and secrete pepsin enzyme from gastric mucosa. The pepsin is a protease enzyme, it can break down protein. HCl is secreted by the gastric mucosa in carnivorous fishes creating the low pH because the enzymes are active in acidic medium (pH 2). The trypsin enzyme is present in the extract of pancreas of some elasmobranchs. The trypsin is secreted by pancreas. The inactive form of this enzyme trypsin - ogen is known as zymogen. It is to be converted into active enzyme i.e. trypsin byan enzyme enterokinase. The enterokinase enzyme is exclusively secreted by intestine of fish. In the Cyprinids, stomachless fish, protease compensation is supplemented by some intestinal enzyme known collectively as erypsin. The intestine secretes amino peptidases.These act on terminal amino acid called as exopeptidases and those act on central bonds are called as endopeptidases.