Meeting Abstract
Mozambique tilapia (Oreochromis mossambicus) are incredibly stress tolerant with respect to environmental salinity, hypoxia, and ammonia concentrations. However, previous work has shown that they have difficulty with low temperature acclimation. We quantified the effects of acclimation temperature and salinity on the thermal tolerance of tilapia as assessed by Critical Thermal Maxima (CTMax) and Critical Thermal Minima (CTMin). During thermal challenges, we observed two unexpected behaviors; Ventilation Cessation Behavior (VCB) and Aquatic Surface Respiration (ASR), and we concluded that the use of these extended thermal scope in both freshwater (FW) and two-thirds seawater (SW). ASR has been previously observed in this and other species in response to oxygen poor water, but its use in response to thermal stress was unexpected. VCB was defined as the cessation of opercular movement for greater than 15 seconds and its observation was completely novel. Both behaviors limit the exposure of the gill epithelium to a waterborne stressor, but VCB likely has repercussions with respect to oxygen homeostasis. ASR was the more preferred behavior in CTMax trials, and VCB was preferred for CTMin, when oxygen demand was reduced. We hypothesize that this behavior potentially underlies the impressive stressor tolerance of this species. Previous work has shown that whole-animal oxygen consumption was inversely proportional to environmental salinity, and that ATPase activity was also reduced in liver and brain extracts under these conditions. The recent observation of VCB is a potential explanation for those findings. To investigate this further, we have monitored tilapia behaviors and oxygen consumption during a series of stressor exposures to determine which stressors elicit VCB (or ASR) and what the physiological consequences of this behavior may be.
