Using orthogonal array design (L9) for optimization of selected dietary supplements (vitamin C, astaxanthin, and soybean lecithin) in Caspian trout (Salmo caspius) broodstocks

The present study was designed to evaluate the effects of different dietary supplements on the reproductive and physiological performance of Caspian trout (Salmo caspius) using an orthogonal array design (L9: 3³). For this purpose, 72 broodstock (with an average body weight of 2.5 kg) were fed nine experimental diets containing three levels of vitamin C (VC); 0, 300 and 700 mg/kg diet, astaxanthin (AX); 0, 50 and 100 mg/kg diet and soybean lecithin (SBL); 0, 6 and 9 % for 16 weeks prior to spawning. Higher absolute and relative fecundity, and fertilization rates were observed in fish fed diets containing AX ₍₁₀₀₎ + SBL _{(%6 and %9)} and VC ₍₇₀₀₎ + SBL _{(%6 and %9)}, respectively, compared to the control group (p < 0.05). The fatty acid, VC and AX contents of fish eggs were also significantly affected by the dietary supplements (p < 0.05). Innate immunity indices (serum lysozyme activity, alternative complement, and total immunoglobulin content) showed significant differences (p < 0.05) among the experimental groups and their highest levels were observed in fish fed with VC ₍₃₀₀₎ + SBL _(%9) supplemented diet. In addition, fish fed the diets containing AX ₍₁₀₀₎ + SBL _(%9) and VC ₍₇₀₀₎ + SBL _(%6) revealed higher serum antioxidant enzyme activity (superoxide dismutase, catalase, and glutathione peroxidase) compared to other experimental groups (p < 0.05). In conclusion, VC _300/700 + AX _{100 +} SBL _(9 %) was an effective combination of dietary supplements for improving the reproductive and physiological responses of Caspian trout.