The impacts of disturbance cue on hypoxia tolerance and thermal tolerance in an African cichlid.

Investigating effects of co-occurring biotic and abiotic stressors on freshwater fishes is crucial to understand how they are coping with environmental change. In this study, we used disturbance cue produced from conspecifics subjected to a simulated predator chase to examine impacts of predation risk on the thermal- and hypoxia tolerance of female Pseudocrenilabrus multicolor, a mouth-brooding African cichlid. Using a series of thermal and hypoxia tolerance trials, we tested 1) how acute exposure to disturbance cue impacts thermal tolerance, 2) how acute exposure to disturbance cue impacts hypoxia tolerance, and 3) how concurrent exposure to warming, hypoxia, and predation risk alters their response. Acute exposure to disturbance cue during normoxia thermal tolerance trials increased critical thermal maximum (CTMax) and decreased agitation temperature (TAg) compared to the water control. When fish were exposed to disturbance cue during hypoxia tolerance trials, the dissolved oxygen level at which they initiated aquatic surface respiration (ASR) was lower than when exposed to water. Finally, acute exposure to disturbance cue during thermal tolerance trials run under hypoxia did not impact CTMax and TAg but elicited a lower temperature at first ASR and increased use of ASR compared to when given the water control. Overall, this suggests that exposure to disturbance cue may increase both thermal and hypoxia tolerance of P. multicolor. However, when these stressors co-occur, exposure to disturbance cue no longer conferred them a thermal tolerance advantage, and the fish appeared more stressed as they relied on ASR more often and at lower temperatures. Therefore, predation risk may be perceived and reacted to differently by prey when multiple abiotic stressors are also present.