Inhibitory effect of Pistia tannin on digestive enzymes of Indian major carps: an in vitro study.

Aquatic weeds are one of the major unconventional feed ingredients tested for aquafeed formulation. Tannin content in the water lettuce, Pistia, has been quantified (26.67 mg g(-1); dry weight) and graded levels of which (12.5-200 μg) have been incorporated in the reaction mixtures to evaluate any change in the in vitro activity of the principal digestive enzymes from the three Indian major carps (IMC), namely rohu (Labeo rohita), catla (Catla catla) and mrigala (Cirrhinus mrigala). Result of the experiment revealed that the Pistia tannin (PT) significantly inhibit/lower the activities of the digestive enzymes from three IMCs in a dose-dependent manner, even at very low concentration. Significant variation in the reduction of the enzyme activities was noticed between the three fish species, as well as between the three enzymes studied. Among the three species studied, digestive enzymes from L. rohita were found to be the most sensitive to the PT, whereas enzymes from C. catla were found to be comparatively least affected. On the other hand, protease and lipase activities were comparatively more affected than the amylase activity. The results of the study suggest that more stress should be given on the elimination of tannin while incorporating feed ingredients of plant origin in fish diets.