Effects of dietary protein and energy levels on growth performance, feed utilization and body composition of juvenile shirbot Barbus grypus (Heckle, 1843)

Shirbot (Barbus grypus) as a species with high potential for aquaculture development recently propagated artificially in South Iran Aquaculture Research Center to extend the species diversity in polyculture system. To provide an effective economic diet for this species 9 experimental diets containing three crude protein levels (250, 300, and 350 g kg (-1)) and three metabolizable energy levels (10.46, 12.55 and 14.64 MJ kg (-1)) were fed to triplicate groups of shirbot juvenile fish (initial body weight of 29.68 +/- 0.19). Three aerated tanks were randomly assigned to each treatment, stocked with 15 juvenile fish and reared for a 60-day period. The preferential diet, which was diet 4, (300 g kg (-1) CP and 10.46 MJ kg (-1) ME) exhibited the best growth and feed utilization performances. Fishes fed diet 4 showed higher weight gain, feed efficiency ratio and survival rate with a significant difference (P<0.05) for WG and FER than other diets except diet 2. It was revealed that increase of CP level in the diet leads to an increase of crude lipid and fiber in the body composition of the fish, but adverse results were obtained when diet ME was increased. Apparent Net Protein Utilization value was increased when the diet protein and energy level were low but the difference was not significant (P>0.05). It was found that varying levels of CP and DE in the diets did not significantly affect the body composition of the fish (P>0.05) except for the CF. Comparison between varying levels of dietary protein and energy on the growth, feed utilization and body composition of Barbus grypus indicated that 250 to 300 g kg -1 CP and 10.46 MJ kg -1 ME could be the preferential dietary levels for this species in the juvenile stage.