Temperature alters thermal tolerance and physiological response to simulated angling in paddlefish

Global climate change has led to the decline of many recreational and commercial fish species. American Paddlefish (Polyodon spathula) support important fisheries across the United States and can experience angling and release across a range of temperatures due to current management regulations. Currently, the impact of thermal variation on paddlefish has not been defined, precluding managers from making thermally-informed decisions related to the timing and duration of angling and harvest seasons. Therefore, we quantified the response of paddlefish chased to exhaustion and air-exposed across a range of temperatures. To accomplish this, juvenile paddlefish were acclimated to 13, 17.5, and 22 °C. Fish were then subjected to a simulated angling interaction and allowed to recover for 0.5 h, 4 h, or 8 h to evaluate recovery of physiological parameters. Following exercise, recovery profiles differed among acclimation temperatures, with paddlefish acclimated to the warmest temperature (22 °C) having prolonged recovery of plasma lactate, compared to fish experiencing cooler temperatures (13.0 °C and 17.5 °C). A second group of paddlefish from each temperature was subjected to a critical thermal maximum test (CT_max). Paddlefish CT_max was influenced by acclimation temperature, but experienced an upper thermal limit, with fish gaining a small but non-significant increase in thermal tolerance when acclimated to temperatures above 17.5 °C. Together, results indicate that paddlefish experiencing warmer water temperatures have reduced performance relative to cooler fish, suggesting that angling or release at temperatures over 17.5 °C will result in an extended recovery period, and paddlefish may have limited capacity for acclimation to warmer temperatures.