Similarities in metabolism and hypoxia tolerance of native and non-native florida freshwater fishes remain consistent in climate change scenarios

As climate change contributes to rising water temperatures and lower dissolved oxygen concentrations to freshwater bodies, it has become critical to understand how these parameters will affect ecosystems with established non-native species as part of a worldwide freshwater extinction crisis. Fishes of the family Cichlidae are the most pervasive, non-native fishes in the Florida Everglades and may expand their range under a changing climate. To understand how physiological responses may vary compared to native fishes, the metabolism and hypoxia tolerance of non-native blue tilapia Oreochromis aureus was compared to native bluegill Lepomis macrochirus when acclimated across a range of seasonal and IPCC-projected temperatures. Intermittent-flow respirometry was used to determine the maximum metabolic rate, standard metabolic rate, aerobic scope, and critical oxygen saturation of each species at 22, 30, 32, and 34 °C. None of these metrics significantly differed interspecifically, indicating strong physiological similarity and an unlikeliness of competitive exclusion to occur based on these traits. Maximum metabolic rate and aerobic scope significantly increased with temperature, but standard metabolic rate and critical oxygen saturation were unaffected, reflecting an increase in energy availability and no change in hypoxia tolerance with rising temperatures. Overall, both species are expected to withstand near-future conditions with little-to-no metabolic disadvantage. Metabolic similarity between these species suggests that cichlid establishment in Florida may be driven instead by reproductive and behavioral traits. Future research should examine whether metabolic similarities to cichlids continue to be present amongst centrarchids in temperate environments in the context of future range expansion.