Effects of temperature acclimation on the critical thermal limits and swimming performance of Brachymystax lenok tsinlingensis: a threatened fish in Qinling Mountain region of China

Brachymystax lenok tsinlingensis is an endangered teleost fish species that occurs in the Qinling Mountain region of China. It also happens to represent the southernmost distribution of an endemic Salmonid fish worldwide. Recently, the habitat of this species shifted towards a higher altitude presumably because of climate change, indicating that this species might be suffering from thermal stress. However, information on the thermal physiology of this species is extremely limited. Accordingly, we investigated the effects of acclimation temperature (6, 12, and 18 °C) on ecologically relevant end points such as critical thermal limits, swimming performance and metabolic rate. Our results showed that elevated acclimation temperatures resulted in increased thermal tolerance and decreased swimming efficiency. High temperature (i.e., 18 °C) did not have a marked effect on the critical swimming speed and the maximum metabolic rate but caused an increase in the energetic cost of transport compared with the results at 12 °C. Interestingly, we found that both the acclimation response ratio and the critical thermal maxima of B. lenok tsinlingensis were higher than that of many other Salmonidae fishes, suggesting that this species responds plastically to temperature changes and has a high thermal tolerance. These characteristics are hypothesized to be related to the southernmost distribution of this species.