Effects of predation stress and sex on growth, metabolism, personality traits, and reproductive investment in the rosy bitterling (Rhodeus ocellatus).

Abstract

Despite extensive research on predator-prey interactions, there remains limited understanding of how fish balance growth, reproduction, and survival under predation risk, and whether males and females employ distinct strategies in energy allocation and risk avoidance. To address this gap, we investigated the effects of chronic non-consumptive predation stress on the rosy bitterling (Rhodeus ocellatus), using the northern snakehead (Channa argus) as a natural predator. Rosy bitterlings were exposed either to no predation (control) or to persistent predator presence separated by a mesh barrier. We then measured specific growth rate, standard metabolic rate, routine metabolic rate, maximum metabolic rate, aerobic scope, boldness, activity, aggression, sociability, and gonad mass. The results indicated that while predation stress did not significantly affect growth, metabolism, or personality traits in either sex, it led to a significant reduction in gonad mass in males. This suggests that under predation risk, male rosy bitterlings decrease reproductive allocation, indicating a strategic reallocation of resources away from reproduction, potentially to maintain somatic condition or other unmeasured traits that enhance survival. Furthermore, sex-specific differences were evident: male rosy bitterlings exhibited higher specific growth rate, maximum metabolic rate, aerobic scope, and sociability than females, likely reflecting their larger body size, brighter coloration, greater exposure to predation, stronger sexual selection pressures, and divergent reproductive strategies compared with females.