Comparative assessment of thermal tolerance in rabbitfish (Siganus fuscescens) following acclimation to two different temperatures.

Climate change and coastal thermal pollution are increasingly threatening marine fish populations, yet species specific thermal tolerance data remain limited for many economically important species. This study evaluated the thermal tolerance of rabbitfish (Siganus fuscescens) by comparing fish acclimated to 23 ℃ and 29 ℃ using both the Critical Thermal Maximum (CTmax) and Upper Incipient Lethal Temperature (UILT) protocols. The findings revealed that in CTmax experiments, fish acclimated at 23 ℃ showed a significantly lower in CTmax and semi-lethal temperature as heating rates increased from + 2 to + 10 ℃/h. In contrast, the 29 ℃ acclimation group showed inconsistent thermal tolerance patterns: absolute lethal temperatures were higher than the 23 ℃ group, yet CTmax was lower under most heating rates. Two-way ANOVA confirmed significant effects of acclimation temperature, heating rate, and their interaction on CTmax. UILT results revealed a semi-lethal temperature of 33.4 ℃ for the 23 ℃ group and 33.6 ℃ for the 29 ℃ group. However, the 29 ℃ group showed lower survival stability at high temperatures. These results provide quantitative multi-rate thermal tolerance thresholds for rabbitfish, allowing for more accurate and ecologically realistic assessments of thermal pollution impacts.