Effects of Temperature and Salinity on Podocyst Recycling of the Edible Jellyfish Rhopilema esculentum (Kishinouye, 1891)

Abstract

As one of the edible jellyfish species, Rhopilema esculentum (Kishinouye, 1891) is a traditional fishery resource and an important economic aquaculture species in China. However, facing the current situation of natural resources exhaustion and problems of breeding population frequent disease, quantity, and quality of seedlings in artificial breeding cannot satisfy the market demand. Temperature and salinity have been considered to play crucial roles in regulating R. esculentum asexual reproduction. This study examined the combined effects by exposing post-preserved R. esculentum podocysts (preserved at 2 ± 1 °C for more than 12 months) to three variable temperatures (simulated temperatures increasing from different starting dates of 14.5 °C on 1 April, 18 °C on 1 May, and 23.2 °C on 1 July, respective to natural levels) and three salinities (20, 25, and 30). Podocyst excystment, the start time of strobilation, duration of strobilation, and cumulative ephyra numbers were tested for 45 days and transfer rates from podocysts to ephyrae were analyzed to assess the most optimal combination of temperature and salinity. The results showed that podocyst excystment and ephyrae production occurred in all treatments. Higher temperature and lower salinity significantly facilitated the podocyst excystment and accelerated the start time of strobilation (p < 0.05). Significantly greater ephyra numbers were produced with lower salinity (20 and 25) and temperatures increasing from 18 °C on 1 May to natural levels (p < 0.05). There were significant interactions between temperature and salinity on the cumulative ephyra numbers and transfer rates from podocysts to ephyrae (p < 0.05). These results suggested that R. esculentum podocysts for long-term preservation at low temperature could be recycled. Temperature and salinity regulation can affect the number and time of R. esculentum seedlings to achieve high production and satisfy the market demand for real-time seedling supply. This conclusion would provide a scientific basis for the innovative methods of sustainable utilization of the edible jellyfish (R. esculentum) resources.