The effect of feeding with hydroalcoholic extract of Spirulina platensis on the growth and immune responses of Rainbow trout (Oncorhynchus mykiss) fry

Rainbow trout (Oncorhynchus mykiss) is the most economically important farmed species in Iran, whose intensive culture is associated with various stresses and makes the fish susceptible to various diseases. Using natural immune stimulants is one of the most effective ways to boost immunity and prevent diseases in fish. Spirulina platensis contains protein, vitamins, minerals, essential amino acids, fatty acids and antioxidant pigments such as beta-carotenoid and is considered as a growth stimulant, probiotic and immune system booster in aquatic animals. The present study was conducted in order to investigate the effect of hydroalcoholic extract of spirulina platensis algae on growth and immune responses of rainbow trout (O. mykiss) fry. A completely randomized experimental design was developed with five test groups including commercial diet as control along with ۲, ۴, ۶ and ۸% hydroalcoholic extract of spirulina algae each containing three replicates. two thousand and four hundred rainbow trout with average initial weight of ۲۰±۰.۵ g were assigned to ۲۰ experimental rectangular polyethylene pools (v= ۰.۳m۳). the adaptation and expriment periods were ۱۵ and ۶۰ days, respectively. Biometry performed once every ۲۰ days. Rainbow trout fed by ۸% S. platensis (treatment ۵) showed a significant difference in percentage of the condition factor (۱.۱۶±۰.۰۱), Growth Rate (۰.۴۱±۰.۰۲), Specific Growth Rate (۰.۳۸±۰.۰۱۵), Lysozyme Activity (۲.۷۷±۰.۱۲ mgL-۱) and the survival to oxygen depletion (۶۲.۹۶±۱.۸۵), temperature (۵۷.۴۰±۴.۸۹) and salinity stresses (۷۴.۰۷±۱.۸۵) with the other groups (p<۰.۰۵). Adding ۸% S. platensis hydroalcoholic extract as a food supplement was found to be improved the growth, and immune responses performance in rainbow trout fry.