Effects of thermal acclimation on swimming performance, metabolic rate and the thermal sensitivity of the mitochondria function in juvenile Paddlefish

ABSTRACT Objective Freshwater systems have undergone major changes relative to their hydrologic profile, thermal regime, habitat, and connectivity due to anthropogenic causes. Migratory species are particularly susceptible to such changes given the distances that they travel and the diversity of habitats occupied through their life history. Because of this, it is becoming increasingly important to understand freshwater species’ behavior and physiology to help facilitate their up- and downstream passage past physical and hydrological barriers. Here, we use a combination of approaches, including an enzyme assay that measures the reduction of oxygen in the mitochondria to evaluate the potential thermal tolerance of juvenile (<1 year old) Paddlefish Polyodon spathula acclimated at three temperatures (12, 20, and 25°C). We also used critical swimming speed trials to determine the swimming capacity and respiration rate of juvenile Paddlefish that were acclimated to those three temperatures. Methods We collected skeletal muscle samples from three areas of each fish (dorsal epaxial white skeletal muscle, abdominal white hypaxial skeletal muscle, and a combination of epaxial and hypaxial skeletal muscle tissue [mix of white and red fibers] from the caudal peduncle) to determine whether the estimated enzymatic thermal tolerance was different across tissue types for potential future application to field-collected adult Paddlefish. Results The temperatures at peak enzymatic activity differed across tissue these collection sites (range: 23.12–35.55°C), suggesting that tissue collection site should be carefully considered. Critical swimming speed did not vary significantly across acclimation temperatures (mean ± SE = 40.4 ± 3.03 at 12°C, 59.18 ± 7.08 at 20°C, and 50.13 ± 11.56 at 25°C). Although respiration rate increased with swimming speed, there were no significant differences in maximum metabolic rate across acclimation temperatures during critical swimming trials. Conclusions These data contribute to filling our knowledge gaps concerning the metabolic demands, swimming behavior, and thermal sensitivity of juvenile Paddlefish and suggest that nonlethal approaches may be possible.