The effects of different dietary levels of organic and inorganic selenium on some growth performance and proximate composition of juvenile rainbow trout (Oncorhynchus mykiss)

Selenium, a trace mineral complement is used as cofactor of antioxidant enzymes that protects fishes against environmental stress agents and enhances performance in fishes. In this study the different levels of organic and inorganic source of  selenium were included in juvenile rainbow trout diet to evaluate feed conversion ratio (FCR), specific growth rate (SGR), weight gain percent (WG), condition factor (CF), survival rate (SR) and proximate analysis of the fillet during ۶۰ days of the experiment. The fishes were allotted to ۹ treatment groups including, Tc the fishes were fed diet without any selenium, control group, To۱, To۲ ,To۳ and To۴ the fishes were fed different dosages of inorganic selenium and Ti۱, Ti۲, Ti۳ and Ti۴ those were fed different dose of inorganic Se in their diet. Results showed that To۴, showed the highest level of WG from ۵۰±۲.۸ to ۱۶۸.۵۴± ۲۵.۵۶ g in comparison to Tc (۱۳۴.۳۸± ۲۷.۲۶g) (p<۰.۰۵). Average initial total length of fishes (۱۹± ۱.۱۲ centimeters) increased to ۲۱.۱± ۱.۱۲ cm in Tc and ۲۲.۴۶± ۱.۲۵ cm in To۴ significantly (p<۰.۰۵). Among all treatments, FCR, SGR, WG, CF and SR were improved in To۳ group. Also carcass protein increased in To۴ (۳۲.۵۸±۱.۲۲%) on the contrary of Ti۴ (۲۲.۴۳±۱.۵۱%) (p<۰.۰۵).  As a general conclusion, dietary incorporation of organic selenium at ۰.۴۵ mg/kg showed satisfactory results in some growth parameters and was a useful supplement in salmonid fish diets.