Physiology of Finfish and Shellfish (2+1)

4.3.1.2 Digestion of carbohydrates

The enzymes which break down the carbohydrates in the gut of fishes are carbohydrases. They are amylase, lactase, saccharases/sucrease and cellulase. The most important enzyme is amylase which acts on starch, which break down to maltose and then to glucose by the process of digestion. The starch is digested into glucose by amylase and maltase.

Amylase Maltase

Starch---------------→ Maltose ---------------→ Glucose

In those fishes in which sucrose has been reported, the effect as follows:

Sucrase

Sucrose ---------------→Glucose+ Fructose

The amylase is secreted from the pancreas in carnivorous fishes, but in herbivorous fishes, the presence of this enzyme is reported from the whole gastrointestinal tract as well as from pancreas. In tilapia, the herbivorous, the amylase is present throughout the alimentary tract.

Blood glucose is converted with the aid of insulin, to muscle glycogen. Although clear details are wanting, but excess of glucose enters the blood from digestive tract, the surplus is converted to glycogen in liver. The fishes possess endocommensal bacteria containing an enzyme, the cellulase, which breakdown the cellulose plant material instead of passing out through faeces.