Spirulina platensis with proteins, vitamins, minerals, essential amino acids, fatty acids and antioxidant pigments such as beta-carotenoid, is considered a growth stimulant, probiotic and immune system booster in aquatic animals. The present study was conducted to investigate the effect of feeding with different percentages of hydroalcoholic extract of spirulina algae on the growth indices and some immune responses of juvenile rainbow trout (Oncorhynchus mykiss). 2400 rainbow trout fry were randomly divided into five test groups, including 1 control group (commercial diet with no added spirulina algae extract), 2 to 5 test groups with commercial diet containing 2, 4, 6, and 8 percent of the extract of hydroalcoholic spirulina algae were fed, respectively. The average weight of the fish at the beginning of the study was 20 ± 0.5 grams and they were separated into 20 rectangular polyethylene pools of 300 liters and after two weeks of adaptation to the farm conditions to measure the growth and safety indices for 60 days under maintenance control conditions and biometry was done once every 20 days. Comparison of Mean (±standard error) of the indices calculated at the end of the period, respectively: percentage of obesity coefficient (1.16 ± 0.01), growth rate (0.41 ± 0.02), specific growth rate (38 ± 0.015 0.0), lysozyme activity (2.77 ± 0.12 mg/liter) and survival percentage at oxygen, thermal and salinity tensions, 62.96±1.85, 57.40±4.89 and 74.07±1.85, respectively which showed a significant difference in treatment 5 (8% spirulina algae extract) from other test groups (p < 0.05).Therefore, the use of hydroalcoholic spirulina extract at 8% as a supplement in the calculated diet of rainbow trout fry significantly improves growth and safety indices.
Keywords: Spirulina, Rainbow trout, Growth, immunity, Algae, Diet