Growth performance, plasma parameters and liver antioxidant enzymes activities of Rainbow trout (Oncorhynchus mykiss) juvenile fed on Spirulina platensis extract

The purpose of this study was to evaluate the physiological responses of Rainbow trout fed on diets supplemented with methanolic extract of Spirulina platensis. 150 fish with a mean initial weight of 12.6±0.3 g were randomly divided into five groups. The juveniles were fed for 8 weeks with the diets containing 0, 250, 500, 1000 and 2500 mg of S. platensis extract per kg of diet. After eight weeks, 12 fish from each treatment were subjected to confinement stress. It has been shown that 250 mg of the algae extract per kg of diet resulted in the highest final weight and lowest feed conversion ratio in fish. There was no significant difference between treatments in fat, protein and moisture contents. The results showed that three hours after the air exposure and confinement stress, minimum (2.42 mg dl-1) and maximum (6.18±2.5 mg dl-1) levels of plasma cortisol were observed in 2500 and 500 mg kg-1 treatments, respectively. Moreover, the minimum (66±14 mg dl-1) and maximum (168±18 mg dl-1) level of glucose has been observed in 0 and 500 mg kg-1 treatments, respectively. After eight hours, Plasma cortisol and glucose have showed the highest level in 500 mg kg-1 treatment. There was no difference in lysozyme and catalase enzyme activities, but higher Spirulina extract in diet led to an increase in superoxide dismutase enzyme activity in the liver of Rainbow trout. This study suggests that addition of 250 mg kg-1 of Spirulina extract to Rainbow trout diet can improve growth performance and stress condition.