The energetic costs of escaping predation in wild, schooling white mullet ( <i>Mugil curema</i> )

Although predation is a major driver of group living across taxa and the anti-predator benefits of grouping are well established, the energetic costs experienced by groups under predation remain largely unexplored. In the current study, we use wild white mullet (Mugil curema) to provide real-time quantification of the energetic cost of escape in schooling fish using intermittent closed-loop respirometry. We found that small groups exposed to predators showed a 53.8% increase in their organismal metabolic rate (ṀO2) compared with groups without predator exposure. When we evaluated antipredator behaviors such as escape response, group cohesion and displacement of the group centroid, we found a positive but insignificant correlation to energetic costs. We then investigated whether escape responses are socially modulated by comparing the energetic costs of escape across: (i) solitary individuals, (ii) solitary individuals with visual access to a group, and (iii) groups. We found that escape frequency and energetic costs to predation were comparable across social contexts, suggesting that escape behavior may largely reflect an intrinsic survival response rather than being strongly modulated by social context. Furthermore, we found that fish exposed to predators showed markedly reduced levels of feeding, suggesting that predation constrains energy acquisition in addition to imposing direct energetic costs. Our results provide a direct quantification of the energetic costs of escape in a schooling fish, offering new insights into the physiological trade-offs underlying collective antipredator defenses.