Thermal tolerance, safety margins and acclimation capacity assessments reveal the climate vulnerability of large yellow croaker aquaculture

With the ongoing climate change, marine aquaculture and other food production sectors will face new significant challenges in the next century. Despite the importance of these new challenges, understanding the dynamic thermal tolerance and thermal safety status of some major culture species remains scarce, including large yellow croaker (Larimichthys crocea), the most productive mariculture fish in China. Here, we conducted a relatively complete thermal biology assessment of cultured large yellow croaker using long-term acclimation experiments, critical thermal testing and the collected habitat sea surface temperature (SST) data. Changes in body size, oxidative stress and metabolic biomarkers during acclimation were also measured to evaluate the effects of prolonged thermal stress on performance. Results showed that the critical thermal limits of large yellow croaker acclimated at 11-30 degrees C ranged from 5.27 degrees C to 36.64 degrees C, and the total thermal tolerance zone was 444.74 degrees C-2. Thermal limits increased as acclimation temperature rise, and the estimated acclimation response ratios ranged from 0.32 to 0.63, showing obvious thermal plasticity. The estimated post-acclimation thermal sensitivity values (0.80-1.28) for large yellow croaker acclimated at 11-30 degrees C were close to 1, and the heat-(5.78 degrees C) and cold -thermal safety margins (6.33 degrees C) were both high, showing sufficient thermal tolerance to cope with current observed highest SST and the predicted SST caused by climate change. However, performance results showed that long-term exposure to 30 degrees C would induce energy redistribution and tradeoffs between health/growth and heat tolerance, leading to significantly decreased body weight and increased superoxide dismutase activity in the gill. This result indicates a potential disadvantage of growing large yellow croaker in floating sea-cages, because the shallow culture depth, high density and limited moving spaces in this farming mode make the fish susceptible to fluctuations in SSTs, constrain their ability in behavioral thermoregulation, and increase the risks of hypoxia and disease infections. Thus, these tradeoffs may make the current floating sea-cage farming more vulnerable to elevated temperatures on production. Finally, since our recorded highest in situ SST and warming rate (in summer) have reached up to 30.1 degrees C and 1.2 degrees C/d, we propose that the large yellow croaker farms currently operating in the main producing area of China are already at the risk of summer heatwaves. In the future, more efforts should be made to the selection of heat-resilient strains or the exploration of alternative farming systems in large yellow croaker aquaculture industry to avoid or mitigate potential production decline.