Optimum growth temperature declines with body size within fish species

According to the temperature-size rule, warming of aquatic ecosystems is generally predicted to increase individual growth rates but reduce asymptotic body sizes of ectotherms. However, we lack a comprehensive understanding of how growth and key processes affecting it, such as consumption and metabolism, depend on both temperature and body mass within species. This limits our ability to inform growth models, link experimental data to observed growth patterns, and advance mechanistic food web models. To examine the combined effects of body size and temperature on individual growth, as well as the link between maximum consumption, metabolism, and body growth, we conducted a systematic review and compiled experimental data on fishes from 52 studies that combined body mass and temperature treatments. By fitting hierarchical models accounting for variation between species, we estimated how maximum consumption and metabolic rate scale jointly with temperature and body mass within species. We found that whole-organism maximum consumption increases more slowly with body mass than metabolism, and is unimodal over the full temperature range, which leads to the prediction that optimum growth temperatures decline with body size. Using an independent dataset, we confirmed this negative relationship between optimum growth temperature and body size. Small individuals of a given population may, therefore, exhibit increased growth with initial warming, whereas larger conspecifics could be the first to experience negative impacts of warming on growth. These findings help advance mechanistic models of individual growth and food web dynamics and improve our understanding of how climate warming affects the growth and size structure of aquatic ectotherms.

Automated summary

According to the temperature-size rule, warming of aquatic ecosystems is predicted to increase individual growth rates while reducing body sizes of ectotherms. However, there is a lack of comprehensive understanding of how growth and key processes such as consumption and metabolism are affected by temperature and body mass within species. This study conducted a systematic review and compiled experimental data on fishes to examine the combined effects of body size and temperature on growth. The findings suggest that maximum consumption increases slower with body mass compared to metabolism and that optimum growth temperatures decline with body size. These findings are important for advancing mechanistic models of individual growth and food web dynamics and improving our understanding of the impacts of climate warming on aquatic ectotherms.