Optimizing protein and lipid levels in practical diet for juvenile northern snakehead fish ( Channa argus ).

A 3 × 3 factorial feeding trial was conducted to evaluate the production response of juvenile northern snakehead fish ( Channa argus ). Nine diets containing 3 protein levels (45%, 48% and 51%) and 3 lipid levels (9%, 12% and 15%) were formulated and fed to triplicate groups of juvenile northern snakehead (15.78 ± 0.09 g/fish) for 8 weeks. The formulated diets were named as P45L9, P45L12, P45L15, P48L9, P48L12, P48L15, P51L9, P51L12 and P51L15 (P-Protein, L-Lipid), respectively. Fish fed diets with the lowest protein and lipid combination (P45L9) had the lowest growth performance. Weight gains (WG) of fish fed the 4 diets P48L12, P48L15, P51L9, and P51L12 were not significantly different ( P  > 0.05), but significantly higher ( P  < 0.05) than those of fish fed the other diets. Fish fed diets P48L12 and P48L15 had significantly lower ( P < 0.05) feed conversion ratios (FCR) than the rest of the treatments. Protein retentions (PR) among fish fed the diets P45L12, P45L15, P48L12, P48L15, P51L9, and P51L12 were similar and significantly higher ( P < 0.05) than those of fish fed the remaining diets. Protein sparing effect was observed in the treatments when fish was fed diets containing 45% or 48% dietary protein levels with dietary lipid increased from 9% to 12%. Fish fed diets with 9% lipid tended to have lower viscerosomatic index (VSI), hepatosomatic index (HSI), and whole-body lipid. Increasing dietary protein level significantly increased ( P < 0.05) liver moisture and lipid while dietary lipid level increased liver lipid. Intestinal lipase activity increased significantly ( P < 0.05) with increasing dietary lipid and protein levels while intestinal α-amylase and protease activities were not significantly influenced ( P > 0.05) by dietary treatments. Based on these results, the diet containing 48% protein with either 12% or 15% lipid is the optimal for supporting growth and feed utilization of juvenile northern snakehead under the current testing conditions.