Proteolytic activity in the digestive tract of several species of fish with different feeding habits

Proteolytic activity in the gut contents of two cichlids and six cyprinids from an artificial basin in Sri Lanka was measured using a simple film strip method. This comparative study contributes to our general knowledge of digestion in herbivorous fish: 1) Specific proteolytic activity (per ml of gut content) is lower in herbivorous than in omnivorous and carnivorous species. 2) Specific proteolytic activity is negatively correlated with the relative length of the gut, but the time of exposure of ingested food to proteolytic enzymes rises with increasing gut length. This results in more intensive proteolytic digestion in herbivorous fish. 3) Proteolytic enzymes seem to be "reabsorbed" in the hindgut of the fish. The effectiveness of this mechanism rises up to a relative gut length of 2.5-3.0. However, the small species Amblypharyngodon melletinus does not fit this relationship.