The preference for social affiliation renders fish willing to accept lower O₂ levels

Animals are bombarded with information about their environment, and must select and interpret the relevant cues to make behavioral adjustments critical to survival. How animals integrate and balance the many signals they receive about their environment is rarely assessed. We investigated how signals from the social and physical environment interact to influence environmental preferences in the endemic Tanganyikan cichlid, Neolamprologus pulcher. Specifically, we explored how fish respond to the physiological challenge of declining O2 levels in light of embedded social preferences using a modified shuttle box apparatus to test O2 preferences. In the presence of a conspecific, the average (preferred) PO2 and minimum PO2 experienced were significantly lower (14.90 ± 2.13 kPa and 12.35 ± 3.15 kPa, respectively) than in trials without a conspecific (17.18 ± 2.55 kPa and 15.62 ± 3.09 kPa, respectively). Fish with conspecifics also spent more time in the low PO2 zone of the shuttle box, and moved between the high and low PO2 zones less frequently. Hence, O2 preferences were modified, and fish willingly remained in an area of continuously declining O2 availability to associate with a conspecific. Individual O2 preferences during social trials correlated with its excess post-exercise O2 consumption following an exhaustive chase, but not with its aerobic scope, routine O2 consumption rate, or body mass. These results suggest that some aspects of respiratory and metabolic physiology, like the propensity to use anaerobic metabolism, but not others, like O2 transport capacity, underpin some variation in social behavior under environmental stress.