Effects of vitamin C on the foraging and feeding abilities of sea urchins (Mesocentrotus nudus) in relation to collagen content and the TGF-β/Smad pathway

Increased demand for the purple sea urchin (Mesocentrotus nudus) has led to the decline of wild populations world-wide, and has necessitated the further development of aquaculture for this species. In seed production operations, it is essential to integrate appropriate nursery methodology to enhance foraging and feeding ability, and thus achieve maximal growth rates. In this study, an 80 d feeding trial was performed to investigate the impact of vitamin C on the foraging and feeding abilities of M. nudus and the regulatory mechanisms from the perspective of the transforming growth factor beta (TGF-β)/Sma- and Mad-related protein (Smad) pathway. A batch of M. nudus (3.48 ± 0.03 g) were fed either kelp (Saccharina japonica) or one of three dry feeds supplemented with vitamin C (0, 3, or 6 g/kg) in three replicates. The results indicated that M. nudus fed kelp presented better feeding and growth performance than did those fed dry feeds. Among the dry feed groups, the best feeding and growth performance of M. nudus was achieved with the supplementation of 3 g/kg vitamin C. Consistently, the foraging and feeding abilities of M. nudus were markedly elevated by supplementation with 3 g/kg vitamin C and were not significantly different from those of M. nudus fed kelp. The collagen contents of selected tissues (spine joint muscle, Aristotle's lantern muscle, and peristomial membrane) and the expression of genes related to collagen synthesis and regulation (smad nuclear-interacting protein 1 (SNIP1) and TGFβR1 and TGFβR2 genes) in M. nudus in the feed groups were markedly greater than those in the kelp groups. Notably, M. nudus fed feeds with 3 g/kg vitamin C presented markedly greater collagen content in the three selected tissues, more tightly arranged collagen fibers, larger collagen fiber areas, and greater expression of genes involved in collagen synthesis and the regulation of genes in the peristomial membrane. To conclude, vitamin C enhanced the foraging and feeding abilities of M. nudus, possibly by regulating the TGF-β/Smad pathway and collagen synthesis in foraging- and feeding-related organs.