Effects of the defattedSchizochytriumsp. on growth performance, fatty acid composition, histomorphology and antioxidant status of juvenile mirror carp (Cyprinus carpiovar.specularis)

Abstract

Defatted Schizochytrium sp. (DS) is a by-product of algae oil, which is rich in docosahexaenoic acid (DHA). In this study, five DS-supplemented diets, including 0 (DS0), 30 (DS3), 60 (DS6), 90 (DS9) and 120 (DS12) g/kg, were used to evaluate the effects of dietary DS on juvenile mirror carp (Cyprinus carpio var. specularis). A total of 270 fish juvenile mirror carp (8.55 g/tail, eighteen fish per cage) were fed with five isonitrogenous and isolipidic diets for 8 weeks. The results showed that final body weight (FBW), weight gain (WG) and specific growth rate (SGR) first increased in DS6 group (p > 0.05) and then significantly decreased in DS12 group (p < 0.05). There were significantly higher crude protein (CP) and lower crude lipid (CL) levels in whole body and hepatopancreas of fish fed with DS6 and DS9 diets than those with DS0 and DS3 diets (p < 0.05). The level of DHA in the muscle, hepatopancreas and whole body was significantly increased by higher DS-supplemented diets (DS6, DS9 and DS12) than that of the control group (p < 0.05). The atherogenic index (AI) and thrombosis index (TI) in the muscle of all treatment groups were significantly lower than those of the control group, while the hypocholesterolaemic/hypercholesterolaemic fatty acid ratio (h / H) index of treatment groups was significantly higher than that of the control group (p < 0.05).The height of fore-intestinal villi of DS3 and DS6 groups was significantly higher than that in the control group (p < 0.05). Moreover, superoxide dismutase (SOD) activity of the serum and hepatopancreas in DS6, DS9 and DS12 groups was significantly higher than that in the control group (p < 0.05). Analyses based on the special growth rate and antioxidant status index revealed that the suitable DS range was 4.18%–6.00% (41.08–60 g/kg), which could improve the growth performance and health status of mirror carp.