# Vitamin C Promoted Feeding and Growth Rate of Apostichopus japonicus by Increasing Its Digestive Capacity Through a 5-Hydroxytryptamine-Mediated Signaling Pathway

## TL;DR

Adding 5000 mg/kg of vitamin C to sea cucumber diets improves growth and digestion by boosting enzyme activity and serotonin signaling.

## Contribution

The study identifies a 5-hydroxytryptamine-mediated pathway through which vitamin C enhances digestive and growth performance in Apostichopus japonicus.

## Key findings

- 5000 mg/kg VC supplementation significantly increased growth rate and feeding activity in sea cucumbers.
- VC at 5000 mg/kg elevated digestive enzyme activity and mucus secretion, improving food capture and digestion.
- High VC doses (15,000 mg/kg) hindered growth and failed to provide benefits seen at the optimal dose.

## Abstract

Sea cucumbers (Apostichopus japonicus) are economically valuable marine organisms, but their growth in artificial farming is often limited by feeding and digestive efficiency. To address this issue, we conducted a 60-day feeding study to explore how different levels of dietary Vitamin C (VC) affect the growth and physiological performance of A. japonicus. We found that a 5000 mg/kg VC supplement significantly improved A. japonicus growth, as shown by faster weight gain and more active feeding behavior. This improvement was linked to enhanced digestive enzyme activity, increased mucus secretion for better food capture, and healthier intestinal structures. Additionally, 5000 mg/kg VC intake promoted the production of 5-hydroxytryptamine, a key substance that regulates feeding and digestion. In contrast, either VC deficiency or excess failed to provide such benefits and even hindered growth. Our findings offer practical guidance for optimizing A. japonicus aquaculture practices, helping to improve its productivity and sustainability.

To investigate the effects of dietary vitamin C (VC) supplementation at different concentrations (0, 5000, and 15,000 mg/kg) on the growth and feeding performance of sea cucumbers (Apostichopus japonicus), a 60-day feeding trial was conducted. The results demonstrated that supplementation with 5000 mg/kg VC significantly enhanced growth performance, evidenced by a higher specific growth rate and weight gain, along with a shorter feeding initiation time and increased tentacle feeding frequency. Furthermore, the activities of digestive enzymes—including amylase, lipase, and pepsin—were markedly elevated in the intestines of A. japonicus fed 5000 mg/kg VC, accompanied by increased mucus secretion in the oral tentacles. Correspondingly, intestinal 5-hydroxytryptamine (5-HT) levels and the expression of tryptophan hydroxylase (AjTPH) and 5-HT receptor (Aj5-HT4R) genes were significantly upregulated in the same group. In contrast, relatively lower growth performance was observed in the control (0 mg/kg) and high-dose (15,000 mg/kg) VC groups. Histological analysis further revealed that 5000 mg/kg VC increased villus height and width and thickened the intestinal muscle layer. Overall, dietary supplementation with 5000 mg/kg VC enhanced feeding activity, digestive function, and intestinal morphology, thereby promoting growth. However, excessive supplementation (15,000 mg/kg) failed to provide similar benefits and was associated with impaired performance.