Document Type : Primary Research paper
A ninety days feeding experiment was directed to compare the effect of Duckweed (Lemna minor) and soybean, Glycine max (L) meals as a source of protein on the actions of intestinal digestive enzymes of Chinese carps; Grass carp, Ctenopharyngodon idella (Valenciennes, 1844) and Silver carp, Hypophthylmichthys molitrix (Valenciennes, 1844) fingerlings reared in monoculture and polyculture system. Two 35 % protein experimental diets, FSBM (feed containing 21 % soybean meal) and FDW (feed having 21 % duckweed) as a source of protein were prepared and fed for twelve weeks. At the end of trial, the experimental diets showed a significant effect on the activities of intestinal digestive enzymes. There is significant (P<0.001) difference in the intestinal cellulase, protease and amylase enzymes in both Chinese carps. In culture systems, intestinal protease and amylase activities of fingerlings of C. idella fed FDW diets were significantly higher as compared to fish fed FSBM diet. In polyculture system, the intestinal amylase activity of H. molitrix fingerlings was significantly higher when fish offered FDW diet as compared to FSBM diet.The results of this study indicate the usage of L. minor as a protein source in polyculture system enhances the fish digestive capacity than monoculture system.