From solitude to pairs: the role of social setting in modulating locomotor and exploratory behavior in a gregarious freshwater fish

The presence of a conspecific can influence individual behavior due to providing numerous benefits, including increased foraging efficiency, enhanced predator detection, and opportunities for social learning. While these benefits often arise from being in groups, the effects of minimal social exposure remain poorly understood and could help to better interpret ecological and evolutionary processes. We examined how social context (individuals tested alone or in pairs) affects locomotor and exploratory behaviors in the gregarious freshwater fish Squalius cephalus. Fish tested in pairs exhibited higher exploration rates than solitary fish, likely reflecting social facilitation and information gathering. Isolated fish showed elevated average acceleration, suggesting more erratic or stress-related movements. Mobile speed, mobility rate, freezing events, and spatial positioning were not significantly affected. These results demonstrate that even the smallest social context (a single conspecific) can influence behavioral components. Our findings highlight the importance of considering social context in controlled experiments and aquaculture practices, as isolation may produce unrepresentative behavioral baselines.