Effects of Vitamin C Concentration on the Growth and Development of First Instar Juvenile Chinese Horseshoe Crabs (Tachypleus tridentatus) Determined by Transcriptomic and Enzyme Activity Analyses.

Vitamin C (VC) is an essential micronutrient known to significantly promote growth and enhance immunity in aquatic organisms. For crustaceans, dietary VC is a critical requirement for proper development. To assess the effects of VC supplementation on juvenile Chinese horseshoe crabs (Tachypleus tridentatus), first instar juveniles were subjected to various concentrations of VC in the aquatic environment. The objectives of this study were to determine the optimal VC concentration for the growth and survival of juvenile horseshoe crabs based on experimental records; to investigate the effects of VC on their gene expression through transcriptomic analysis; and to examine the impacts of various VC concentrations by measuring enzyme activities. The experimental results showed that the optimal VC concentration for molting was 30 mg/L (medium concentration), while 90 mg/L (high concentration) was optimal for survival. The effects of VC were specifically manifested by up-regulation of cytochrome c-like and down-regulation of ATP synthase F0 subunit 6 and increased alkaline phosphatase levels, which accelerated energy absorption and promoted rational energy allocation. At moderate-to-high concentrations, VC up-regulated the expression of papain family cysteine protease and partially up-regulated β-actin, while down-regulating ribosomal protein L29 (RPL29) and rho-related proteins. This expression profile ensured the precise execution of apoptosis and cell division/differentiation. Additionally, downregulation of RPL39 by VC enhanced translation efficiency. Concurrently, up-regulation of RPLP2, protein component of the small (40 S) ribosomal subunit, and RPL35, along with elevated alkaline phosphatase levels, collectively improved cellular immunity and repair capacity. Overall, these results confirm that VC promotes the growth and development of T. tridentatus.