Effects of soil water content on the survival, antioxidant status, and immune responses of leech (Whitmania pigra) during the overwintering

Leech is an important aquatic animal parasite that poses a great threat to the aquaculture industry. However, leech (Whitmania pigra) is an important traditional Chinese medicine and has been widely used to treat cardiovascular or other chronic diseases. Although there has been a growing interest in W. pigra rearing in the South and East of China, the technology of artificial breeding of W. pigra during overwintering is still imperfect. In this study, various soil water contents (30%, 40%, 50%, 60%, and 70%) were tested on W. pigra during a 104-day overwintering period, and their physiological responses were evaluated. During the trial period, the survival rate of W. pigra varied under different soil water contents and the highest and lowest survival rates were 86.67±5.77 and 23.33±11.55 % at the soil water content of 50 and 70%, respectively. The weight-loss rate of W. pigra decreased when the soil water content increased. The activities of antioxidant enzymes, superoxide dismutase and catalase of the leech at 50% soil water content were lower than those in other groups, however, the highest activities of the immune enzyme, alkaline phosphatase, and lysozyme were obtained in the five groups. These results suggest that soil water content is a key environmental factor that affects W. pigra during overwintering and 50% soil water content is the optimal level for W. pigra during the overwintering period.