Dietary carbohydrate to lipid ratios affect the somatic growth, gonad yield and organoleptic quality of Strongylocentrotus intermedius adults

Gonad yield and quality are crucial for the farming of Strongylocentrotus intermedius adults. A 48-d experiment was performed to explore the influences of carbohydrate to lipid ratios (C/L) on the somatic growth, gonad yield and organoleptic quality of S. intermedius adults. Five formulated feeds with graded C/L (1.49, 2.46, 4.08, 7.27, and 16.49) and kelp ( Saccharina japonica ) (control diet) were prepared, which were named C/L1, C/L2, C/L4, C/L7, C/L16, and kelp, respectively. Three tanks of sea urchins (28.36 ± 0.26 g) were fed one of the diets above. The results suggested that the weight gain rate (WGR) and gonadosomatic index (GSI) of sea urchin adults fed C/L7 were significantly higher than those of individuals fed C/L1, C/L2 and kelp. Based on the quadratic regression analysis on WGR and GSI, the optimal diet C/L of S. intermedius adults was estimated to be 10.91 and 11.24, respectively. The gonad lightness of male sea urchins in the C/L7 group was significantly higher than that of individuals in all dietary groups except for the C/L16 group. The gonad yellowness of male sea urchins in the C/L7 was only significantly higher than that in the C/L16. The gonad hardness, springiness, cohesiveness, chewiness and gumminess of adult sea urchins in the C/L7 were comparable to those in the kelp and C/L4. At all timepoints (0, 6, 12, and 24 h) post cold storage, the gonad superoxide dismutase (SOD) activity of adult S. intermedius fed C/L7 was significantly higher than that of individuals fed kelp, C/L1 and C/L16 from 12 h to 24 h. The gonad catalase (CAT) activity of urchins fed C/L7 was significantly higher than that of individuals fed C/L1–4 at 24 h. The gonad malondialdehyde (MDA) content of urchins fed C/L7 was significantly lower than that fed kelp and C/L1 at all timepoints. Overall, the optimal diet C/L was estimated to be 7.27–11.24 for achieving highest gonad yield and quality of S. intermedius adults. • Based on the WGR and GSI, the optimal diet C/L of adult S. intermedius was estimated to be 10.91 and 11.24, respectively. • S. intermedius fed diets with C/L7.27 showed better color of gonads. • Low or high C/L can damage the gonad texture of adult S. intermedius. • S. intermedius fed diets with C/L7.27 exhibited lower degree of lipid peroxidation and can prolong the shelf life of gonads.