This study was conducted in indoor, aerated plastic tubs to estimate the digestibility of dry matter and nutrients by the carps, Labeo fimbriatus (Bloch, 1795) and Cyprinus carpio Linnaeus, 1758, from three feed ingredients viz., azolla, soybean meal and silkworm pupa incorporated at levels ranging from 0-40% in a diet comprising equal amounts of rice bran and groundnut oil cake using crude fibre as the marker. Activity of the major digestive enzymes was also estimated in the gut of fish at the end of the experimental trial. Utilisation of azolla protein was comparable with that of control diet up to 20% incorporation in both L. fimbriatus and common carp. Major nutrients from soybean were better utilised up to 40% incorporation by the two species. Protein digestibility from silkworm pupae increased at 20% incorporation and decreased at 40% in L. fimbriatus, while fat and nitrogen-free extract digestibility was higher at 20-40% incorporation. In common carp, higher digestibility of protein and fat was recorded at 10-30% inclusion levels of silkworm pupa.

An experiment of 60 days duration was carried out to compare dry matter and protein digestibility of periphyton grown on sugarcane bagasse bundles and a pelleted feed in Labeo fimbriatus (Bloch, 1795). Advanced fingerlings maintained in glass aquaria were allowed to feed on fresh periphyton or pelleted feed (20% crude protein) daily morning, the fecal matter collected following standard procedure and analysed for proximate composition. Acid insoluble ash was used as the reference marker for digestibility estimation. Activity of total protease, trypsin, chymotrypsin, carboxypeptidase - A and B, amylase, lipase and cellulase in the gut of fish was estimated at the end of the feeding trial. Periphyton and pelleted feed showed similar (p>0.05) protein digestibility (92.29 and 89.21% respectively), while total dry matter digestibility was higher (p<0.05) with peiphyton (85.44 and 75.16% respectively). Among the proteases estimated, activity of total protease and carboxypeptidase B was higher (p<0.05) in fish fed periphyton, whereas activity of others showed no difference between those receiving periphyton and pelleted feed (p>0.05). Activity of carbohydrases and lipase was higher in fish fed pelleted feed. Results of the study cleary indicated that L. fimbriatus can efficiently utilise periphyton.