Temperature constrains locomotion and muscle function in two temperate labrids.

Winter quiescence in fishes is not uncommon, however understanding the mechanisms that cause dormancy are poorly understood. This study highlights the physiological stress temperature places on locomotor musculature and its consequences on whole organism locomotion. Cunner and tautog experience temperatures ranging from 0 to 25 °C and enter dormancy at ~10 °C. We aimed to address the question: how do winter temperatures affect steady swimming and muscle contraction kinetics in cunner? Fishes were collected and housed at 5, 10, 15, or 20 °C. Gait transition speed and fin beat frequency were measured at each acclimation temperature. Twitch and tetanus kinetics were recorded from the aerobic locomotor muscle, which is responsible for the power stroke during swimming. Fish acclimated to colder temperatures (5, 10 °C) demonstrated lower gait transition speeds than the warm temperature treatments. Similarly, twitch kinetics were slower in muscle acclimated at ≤10 °C. Locomotor muscle from tautog was significantly slower to contract and relax than cunner when tested at 5 and 10 °C. These results suggest that muscle acclimation differs in these closely related labrids from the same habitat. Additionally, these results suggest that cunner locomotor musculature can maintain greater performance at a wider range of temperatures. Cunner occupy more northern latitudes which likely allows for greater performance shifts in response to temperature. However, when temperatures get cold enough muscle function is reduced, perhaps contributing to their overwintering ecology.