Effects of acclimation temperature on critical thermal limits and swimming performance of the state-endangered bigeye chub hybopsis amblops

Thermal stress can directly affect the survival of fishes and indirectly impact fish populations through several processes, including impaired swimming performance. Bigeye chub Hybopsis amblops is a state-endangered species in Illinois and is disappearing in the northern portion of its native range in North America. Limited temperature tolerance information exists on this species. The aim of this study was to define the impacts of 2 acclimation temperatures on the performance and behavior of bigeye chub. To accomplish this, we conducted 2 assays: critical thermal maximum (CT_max) testing for upper thermal tolerance limits, and swimming performance testing for critical swimming speed (U_crit) and burst swimming ability. With a 5°C acclimation temperature increase from 21 to 26°C, the CT_max of bigeye chub increased from 32.8 ± 0.4°C to 36.4 ± 0.9°C. U_crit was not different across acclimation temperatures, and fish from both acclimation groups could swim up to over 10 body lengths (BL) s⁻¹. Burst swimming duration also did not differ statistically across groups, but bigeye chub from the 26°C group swam 27% longer in duration relative to fish from the 21°C group. Results from this study can help guide the protection and restoration of bigeye chub populations from thermal stressors.