Effects of Dietary Inclusion of Fermented Soybean Meal with Phaffia rhodozyma on Growth, Muscle Pigmentation, and Antioxidant Activity of Juvenile Rainbow Trout (Oncorhynchus mykiss)

This study was designed to test the effects of dietary supplementation of fermented soybean meal (FSM) with Phaffia rhodozyma on growth, muscle pigmentation, and antioxidant activities of juvenile rainbow trout (Oncorhynchus mykiss). Solid fermented soybean meal with P. rhodozyma (FSPH) contained 500 ppm astaxanthin was used as the natural source of astaxanthin in the present study. Four isonitrogenous and isocaloric diets were formulated to contain 0, 50, 75, and 100 ppm astaxanthin (designated as FSPH0, FSPH50, FSPH75 and FSPH100, respectively). Each experimental diet was fed to triplicate groups of fish (18.5 g/fish) to visual satiation twice daily for 10 weeks. Growth performance and proximate composition of muscle were not affected by dietary treatments. Total carotenoid and astaxanthin concentrations in muscle of fish were not affected by dietary treatments. Redness (a*) values of muscle from fish fed the FSPH50, FSPH75, and FSPH100 diets were significantly higher than those fed the FSPH0 diet. Plasma and liver DPPH, hydroxyl, and alkyl radical scavenging activities were not affected by dietary treatments. Plasma total antioxidant capacity of fish fed the FSPH50 diet was significantly higher than that of the FSPH0 group. Fish fed the supplemented diets showed significantly lower catalase activity compare to those fed the unsupplemented control diet. Plasma superoxide dismutase activity in fish fed the FSPH100 diet was significantly lower than that of fish fed the FSPH75 diet. These results suggest that the combination of FSM and P. rhodozyma is a good source of astaxanthin, and that a diet containing 10% of this mixture (equal to 50 ppm astaxanthin) could successfully improve muscle pigmentation and antioxidant status of juvenile rainbow trout.