The effects of dietary supplement of Spirulina platensis on blood carotenoid concentration and fillet color stability in rainbow trout (Oncorhynchus mykiss)

To evaluate the effects of diets including 0, 2.5, 5, 7.5 and 10% Spirulina platensis powder on blood carotenoid concentration (BCC) and fillet color stability of rainbow trout (Oncorhynchus mykiss), a completely randomized experimental design was developed with five triplicate treatments. One hundred and eighty rainbow trout with an average initial weight of 101 ± 8 g were cultured for 10 weeks. BCC significantly increased with increasing the levels of the alga and fish fed 7.5 and 10% S. platensis showed higher BCC compared to the other treatments (p < 0.05). At the end of the experiment, positive relationships were observed between BCC and weight gain, final weight and Specific Growth Rate (SGR), while a negative relationship was found between BCC and Feed Conversion Ratio (FCR). Regression analysis demonstrated a positive relationship between blood level of carotenoid and its final level in the muscle. Fillet color parameters (L, a* and b*) were also highly correlated to BCC in the rainbow trout fed S. platensis. There were no significant differences (p = 0.584) in fillet carotenoid content after two weeks of storage at 4 °C. Although there was no significant difference between carotenoid concentrations of fillet during frozen storage (− 20 °C) up to 3 months, this value decreased after six months (p < 0.05). The present results demonstrate that BCC can be used as an indicator to predict final fillet pigmentation in rainbow trout. Furthermore, carotenoid content in fish fed S. platensis was stable at 4 °C and at least 3 months at − 20 °C.