Effects of microencapsulated vitamin C on growth performance, antioxidant capacity, and innate immunity in planktonic larvae of the Manila clam (Ruditapes philippinarum)

Abstract

Bivalve planktonic larvae are extremely vulnerable to oxidative stress under intensive hatchery conditions, resulting in growth retardation and elevated mortality. This study evaluated the effects of dietary supplementation with microencapsulated vitamin C on growth, antioxidant capacity, and innate immunity in planktonic Manila clam (Ruditapes philippinarum) larvae. An 11-day feeding trial was conducted in cylindrical tanks using a microalgal-based diet and supplemented with 0, 0.086, 0.114, or 0.142 mg of microencapsulated vitamin C powder per gram of larval wet weight. Relative to the non-supplemented control (0 mg g⁻¹ group), larvae fed 0.114 mg g⁻¹ microencapsulated vitamin C showed a 33% increase in weight per tank and a 20% increase in survival rate. Following H₂O₂ exposure, mortality at both 8 h and 12 h was significantly reduced in all vitamin C-supplemented groups relative to the control. In addition, the 0.114 mg g⁻¹ group showed significantly higher superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and increased reduced glutathione (GSH) content, lower malondialdehyde (MDA) content, upregulated Nrf2 pathway genes (nrf2 and keap1), and downregulated gclc and gstp1. In the same group, lysozyme (LZM), phenoloxidase (PO), and alkaline phosphatase (AKP) activities were significantly increased, while NF-κB pathway genes (tlr4, myd88, cox2, ikkα, and nfkb1) were significantly downregulated. Regarding proinflammatory and hypoxia-related factors, tnf-α was significantly downregulated and hif-1α was markedly downregulated in the 0.114 mg g⁻¹ group, whereas il-17 was significantly downregulated in the 0.142 mg g⁻¹ group. Overall, dietary supplementation with 0.114 mg g⁻¹ microencapsulated vitamin C significantly enhanced weight per tank, survival, oxidative stress resistance, and innate immunity in R. philippinarum larvae.