Abstract
Key to predicting the response of fishes to climate change is quantifying how close fish are to their critical thermal limits in nature and their ability to adjust their thermal sensitivity to maintain performance. Here, we evaluated the effects of body size and habitat on aerobic scope (AS) and thermal tolerance of Nile perch Lates niloticus (L.), a fish of great economic and food security importance in East Africa, using respirometry and critical thermal maximum (CTmax) trials. Juvenile Nile perch from distinct habitats (high or low dissolved oxygen concentrations) of Lake Nabugabo, Uganda were exposed for 4.6±0.55 days to a temperature treatment (25.5, 27.5, 29.5 or 31.5°C) prior to experimentation, with the lowest temperature corresponding to the mean annual daytime temperature in Lake Nabugabo and the highest temperature being 3°C higher than the maximal monthly average. As expected, metabolic rates increased with body mass. Although resting metabolic rate increased with temperature, maximal metabolic rate showed no change. Likewise, AS did not vary across treatments. The CTmax increased with acclimation temperature. There was no effect of habitat on maximal metabolic rate, AS or CTmax; however, there was a trend towards a lower resting metabolic rate for Nile perch captured in the low-dissolved oxygen habitat than in well-oxygenated waters. This study shows that juvenile Nile perch maintain a large AS at temperatures near the upper limit of their natural thermal range and provides evidence that Nile perch have physiological mechanisms to deal with acute exposure to thermal stress.
Highlights
Environmental temperature is a key predictor of species distribution that can affect the fitness and performance of individuals (Parmesan and Yohe, 2003; Pörtner and Farrell, 2008).Assuming organisms are adapted to the thermal regime of their environment, their temperature limits and optimum should fall with the thermal range of their natural habitat (Janzen, 1967; Pörtner and Farrell, 2008)
Juvenile Nile perch from distinct habitats of Lake Nabugabo, Uganda were exposed for 4.6 ± 0.55 days to a temperature treatment (25.5, 27.5, 29.5 or 31.5°C) prior to experimentation, with the lowest temperature corresponding to the mean annual daytime temperature in Lake Nabugabo and the highest temperature being 3°C higher than the maximal monthly average
Juvenile Nile perch were exposed to a range of biologically relevant temperatures, with the lowest acclimation treatment corresponding to the mean annual daytime temperature in Lake Nabugabo (25.5°C) and the highest temperature (31.5°C) being 3°C more than the maximal monthly average
Summary
Environmental temperature is a key predictor of species distribution that can affect the fitness and performance of individuals (Parmesan and Yohe, 2003; Pörtner and Farrell, 2008).Assuming organisms are adapted to the thermal regime of their environment, their temperature limits (upper and lower) and optimum should fall with the thermal range of their natural habitat (Janzen, 1967; Pörtner and Farrell, 2008). Such, tropical species are hypothesized to have narrow thermal windows relative to temperate species because they have evolved in relatively constant temperatures (Janzen, 1967). Such narrow thermal windows may pose a significant challenge in the face of predicted global temperature increases, because this may limit the range of thermal increase that permits persistence (Huey and Hertz, 1984). This is true for ectotherms, such as fishes. Tropical fishes (ectotherms that are likely to be thermal specialists) may be vulnerable to climate change (Tewksbury et al, 2008)
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