Effects of temperature and thermal shock on growth and health of southern medicinal leech (Hirudo verbana Carena, 1820)

Abstract

The over-collection pressure on medicinal leech populations, coupled with habitat loss, has led to a decline in natural stocks, emphasizing the need for leech aquaculture and standardized production protocols. The effects of water temperature and thermal shock on leech aquaculture remain unclear, making standardization in leech aquaculture challenging. Understanding these effects is also crucial for assessing the impact of global warming on leech populations. This study investigated the impact of different temperatures and thermal shocks on the growth and health of medicinal leeches through two trials. In the first trial, leeches were cultured at four temperatures (15°C, 20°C, 25°C, and 30°C) to determine the optimal range. A quadratic linear decrease in final body weight was observed (P_Quadratic = 0.001), with higher temperatures leading to increased regurgitation and cannibalism, and a lower proportion of healthy leeches. The optimal temperatures for the growth and health of leeches were found to be 18.7°C (R² = 0.701) and 19.7°C (R² = 0.303), respectively. In the second trial, leeches were kept at 18.7°C and exposed to thermal shocks at six temperatures (3.7°C, 8.7°C, 13.7°C, 23.7°C, 28.7°C, and 33.7°C) during triweekly water changes. No significant differences in final body weight were determined among groups (P_Anova = 0.799). Interestingly, cold thermal shocks reduced regurgitation and cannibalism while increasing the proportion of healthy leeches. These findings highlight temperature and thermal shock as critical environmental factors in leech aquaculture. Maintaining temperatures between 18.7 and 19.7°C appears optimal, and cold thermal shocks may have beneficial effects on leech health.