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) partial pressure of oxygen (Po₂) and minimum Po₂ experienced were significantly lower ([Formula: see text] and [Formula: see text] kPa, respectively) than in trials without a conspecific ([Formula: see text] and [Formula: see text] 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. The O₂ preferences of an individual during social trials correlated with its excess postexercise 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 (such as the propensity to use anaerobic metabolism) but not others (such as O₂ transport capacity) underpin some variation in social behavior under environmental stress.