Thermal Tolerance of Spotted Sea Bass (Lateolabrax maculatus) and Pearl Gentian Grouper (Epinephelus fuscoguttatus Female × E. lanceolatus Male) in Different Environmental Temperatures

Abstract

Seawater cooling is the most common way to cool down nuclear power plants. However, the thermal drainage of nuclear power plants results in sharp rises in local seawater temperatures and, therefore, affects fisheries and ecologies. Therefore, evaluating the thermal tolerance of marine organisms not only provides further insight into their biological characteristics but also holds significant importance for the site selection and construction of nuclear power plants. This study investigated the thermal tolerance of spotted sea bass (Lateolabrax maculatus) and pearl gentian grouper (Epinephelus fuscoguttatus female × E. lanceolatus male) using the critical thermal maximum method. The environmental temperatures for spotted sea bass and grouper in spring, summer, autumn, and winter were 21.6/23 °C, 26.5/25.9 °C, 25.0/25.9 °C, and 14.5/16.6 °C, respectively. Under four seasonal conditions, different temperature rise rates of +2 °C, +4 °C, +6 °C, and +8 °C per hour were set. The maximum critical temperature, initial lethal temperature, absolute lethal temperature, and semi-lethal temperature were recorded for both fish species. The results show that the rates of temperature increase did not affect the thermal tolerance of either fish species. In all seasons, the fish experienced rapid death once they reached the initial lethal temperature. However, there was a significant correlation of season with thermal tolerance in both fish species. For spotted sea bass, the semi-lethal temperature in summer reached about 40 °C, while in winter it was about 35 °C. For pearl gentian grouper, the semi-lethal temperature in summer reached about 40 °C, while in winter, it was about 38 °C. These results remind us that these two fish species have a limited ability to adapt to rapid temperature rises, but appropriate acclimation temperatures can effectively improve their thermal tolerance. Therefore, it is necessary to further consider the potential impacts on these fish species during the site selection and construction process of nuclear power plants.