Dietary tryptophan requirement of northern snakehead, Channa argus (Cantor, 1842)

The optimum dietary tryptophan requirement has not been estimated for northern snakehead (Channa argus Cantor, 1842) despite being considered the main limiting essential amino acid in many cereal grain ingredients. A 70-day feeding trial was carried out to determine the dietary tryptophan requirement using 540 juvenile fish (10.21 ± 0.11 g) randomly distributed into 18 net cages with six treatments and three replicates. Six extruded isonitrogenous (48.56% protein) and isoenergetic (19.72 KJ of gross energy g−1) diets containing 0.19%, 0.30%, 0.39%, 0.48%, 0.59% and 0.68% L-tryptophan were prepared. Fish were hand-fed twice daily at apparent satiation level. The results indicated that final weight, weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), the crude protein content in dorsal muscle, glutamate dehydrogenase activity and glutamate oxaloacetate transaminase activity in liver were significantly improved, with increases in dietary tryptophan up to 0.48%. The content of Methionine, Histidine, Threonine, Glycine, Phenylalanine and Glutamic acid in dorsal muscle of fish was also markedly affected by the dietary tryptophan levels. On the other hand, fish fed with 0.39% dietary tryptophan had the highest pepsin activity, which was significantly higher than that in fish fed with 0.59% and 0.68% dietary tryptophan, however, the glutamate pyruvate transaminase activity significantly increased until the dietary tryptophan level increased to 0.68%. Based on the second-degree polynomial regression analysis of SGR and FE against dietary tryptophan levels, the optimum dietary tryptophan requirement for C. argus was respectively estimated to be 0.46% and 0.45% of the diet, corresponding to 0.95% and 0.93% of dietary protein. •The growth performance and feed utilization of fish were compromised by tryptophan deficient diet.•The growth performance and feed utilization were significantly improved, with increases in dietary tryptophan up to 0.48%.•Dietary tryptophan level affected the content of Methionine, Histidine, Threonine, Glycine, Phenylalanine, Glutamic acid in dorsal muscle.•Based on the results of SGR and FE, the optimum dietary tryptophan requirement for C. argus was respectively estimated to be 0.46% and 0.45% .