Dietary lysine modulates growth performance, haemato-biochemical indices, non-specific immune response, intestinal enzymatic activities and antioxidant properties of rainbow trout, Oncorhynchus mykiss fingerlings

The experimental trial was conducted to assess the appropriate utilization of dietary lysine (Lys) required for Oncorhynchus mykiss fingerlings. Six isonitrogenous (450 g/kg CP) and isoenergetic (20.9 kj 100 g(-1) GE) casein-gelatine based diets supplemented with varying concentrations of dietary Lys (14.0, 16.5, 19.0, 21.5, 24.0. and 26.5 g/kg, dry diet) were formulated. For each incremental level, all diets were randomly distributed in triplicate groups of 20 fish (1.79 +/- 0.06 g/fish; 5.70 +/- 0.42 cm/fish) and were fed in the morning and evening time (08:00 and 17:00 h) at the rate of 5% BW day(-1). After the end of the trial, maximum live weight gain (355.21), protein efficiency ratio (1.69 g/kg), better-feed conversion ratio (1.31) and maximum body protein deposition were recorded at 21.50 g/kg increment of Lys in the diet. Highest body protein, lowest moisture and intermediate fat contents were noted in the fish fed 21.50 g/kg of dietary Lys containing diet, while body ash values did not show any significant (p > .05) changes at each increment of Lys in the diets, except at lower increments, where highest ash content was observed. Hepatosomatic index (HSI) value was noted lowest in the fish fed with diets containing 21.50 g/kg Lys level, while haematological variables also exhibit considerable changes with the addition of each Lys inclusion level. Maximum haemoglobin (Hb), haematocrit (Hct) and red blood cell (RBC) count were also noted at 21.50 g/kg Lys fed diet. Significant variations (p < .05) in plasma variables, non-specific immune system, intestinal enzymatic activities and antioxidant status were also observed in the fish fed with varying dietary Lys containing diets. However, cholesterol, triglycerides, amylase, lipase and superoxide dismutase (SOD) did not show any differences with respect to Lys inclusion levels. Our findings suggest that 21.60 g/kg dietary Lys, corresponding to 48.0 g/kg of dietary protein should be incorporated in the diet of rainbow trout for better growth and efficient nutrient conversion of this species, and also for the improvement in fish health. Collectively, this study indicated that an appropriate amount of Lys improve fish growth, haemato-biochemical parameters, immune response and digestive ability, and also up-regulate the antioxidant status.