Temperature and Food Availability Modify Aggressiveness, Risk-Taking Behaviors and Group Structure in Sparus aurata Early Stages ^†

Increasing ocean temperatures are expected to increase the energy needs of marine organisms, therefore increasing food demand to sustain their metabolism. However, food is limited in the aquatic environment and reduced availability may be intensified by the advance of climate change. Despite the importance of these interacting factors, few studies have explored their combined effects, particularly in early stages of the fish. To address this gap, we investigated how increased temperatures and reduced food availability influence agonistic behaviors, risk-taking, exploratory activity, social preference, and shoal structure in the early stages of Sparus aurata (55 dph). Fish were exposed for two weeks to a cross-experimental design involving two temperature conditions (24 °C and 28 °C) and two levels of food availability (9% and 4.5% of body weight). Our findings revealed that temperature and food restriction significantly reduced aggressiveness. Fish subjected to low food availability, regardless of temperature, exhibited bolder behavior, took greater risks, and engaged in more exploration. Higher temperatures independently increased exploratory activity but did not affect risk-taking. Fish from the four treatment conditions demonstrated a preference to associate with shoals. However, under food restriction, fish were more likely to abandon their shoals, and the low food availability in the high temperature treatment led to looser shoal formations. Overall, our results suggest that food availability has a higher impact than temperature. Fish on low food availability reduced energy expenditure on aggressive behaviors, but engaged in riskier behaviors and increased exploration, probably in an effort to locate food resources.