Effects of dietary protein and lipid content on growth performance and biological indices of iridescent Shark (Pangasius hypophthalmus, Sauvage 1878) fry

Dietary protein and lipid effects on growth, body composition and indices of iridescent Shark Pangasius hypophthalmus (Sauvage 1878) fry were studied using a 4 x 2 factorial design. Triplicate groups of 10 fish per tank, with initial mean weights of 3.54-3.85 g were fed eight isocaloric diets comprising a combination of four protein levels (250, 300, 350 and 400 g kg(-1) or 25%, 30%, 35% and 40%) and two lipid levels (60 and 120 g kg(-1) or 6% and 12%) respectively. The fish were hand-fed to satiety twice daily for 8 weeks. Specific growth rate (SGR) and feed conversion ratio (FCR) showed significant effects (P < 0.05) with variations in dietary protein and lipid. The highest SGR was observed in fish fed 40% protein/12% lipid diet but this value was not significantly (P > 0.05) different from the fish fed 30% protein/12% lipid diet. The FCR was lowest for the 40/12 diet and differed significantly only with the 25/6, 25/12 and 30/6 treatments respectively. The hepatosomatic index (HSI) was significantly affected by the level of protein, but intraperitoneal fat (IPF) showed significant variation due to dietary lipid level. The HSI significantly (P < 0.05) decreased when dietary protein increased from 25% to 30% but increased marginally thereafter. The IPF values increased with increased dietary lipid but decreased with increased dietary protein. Body protein was positively correlated with dietary protein content; conversely, body lipid content decreased with increase in dietary protein. The results of this experiment indicate the presence of a protein-sparing effect of lipid as fish fed 30% protein/12% lipid diet had growth and feed utilization comparable to those fed 40% protein/12% lipid diet.