Assessment of dietary lysine requirement for silver perch (Bidyanus bidyanus) juveniles

A 10-week rearing trial was conducted to assess the lysine requirement of juvenile silver perch, and to evaluate the effects of dietary lysine levels on the morphological measurements, body composition, hematological traits and muscle carnitine status of the fish. Seven isonitrogenous and isolipidic diets were formulated to contain multiple intact proteins and pre-coated crystalline amino acids. l-lysine HCl was supplemented to the experimental diets at the expense of a dispensable amino acid mixture to achieve lysine levels from 0.90 and 2.70% of dry diet. Each diet was randomly assigned to triplicate groups of 10 fish and was fed to apparent satiation five times daily. At the end of the trial, percent weight gain increased with increasing dietary lysine from 0.90% to 2.10%, then the value decreased slightly. A similar trend was observed in the feed efficiency, protein efficiency ratio, productive protein value and daily protein deposition. The condition factor, hepatosomatic index, intraperitoneal fat and viscerosomatic index were markedly affected by the dietary lysine level. Crude protein contents of the whole body, muscle and liver were significantly depressed in the fish fed lysine-deficient diets, while the whole body lipid content was higher in these fish. The hematocrit value, hemoglobin concentration and free lysine levels in plasma were lower in the silver perch given lower lysine diets. Although muscle carnitine status was not clearly affected by the dietary lysine level, the values of free carnitine and acid soluble carnitine tended to be lower in the fish fed lower lysine diets. Based on the quadratic broken-line model, the dietary lysine requirement for maximum growth of the silver perch juveniles was satisfied at 2.32% lysine in the dry diet, corresponding to 5.96% of the dietary protein. Furthermore, 2.06% of chemically available lysine in the diet (equivalent to 5.30% dietary protein) was required for the optimal growth of the fish.