Meeting Abstract
Polyphenic bluegill sunfish Lepomis macrochirus differ in steady and unsteady swimming performance. Pelagic fish demonstrate a higher gate transition speed and lower cost of transport at that transition speed. Similarly, pelagic bluegill show a faster predator escape response. As a result, we hypothesized that pelagic bluegills would have a higher force output and maximum contraction velocity of pectoral, slow and fast myotomal muscles as compared to littoral bluegills. Additionally, given the greater swimming performance of pelagic fish, we hypothesized that they would have higher lactate dehydrogenase and citrate synthase activity when compared to littoral bluegills. To address these hypotheses, we measured maximum force, time to peak force and time to half relaxation for tetanic and twitch contractions. We also performed muscle slack-test protocols to estimate Vmax. For the enzyme analysis, we measured lactate dehydrogenase and citrate synthase activity in the pectoral and myotomal muscles. Generally, littoral and pelagic fish did not differ in their muscle kinematics. However, littoral fish had a higher slow myotomal muscle twitch and tetanic force than pelagic. This indicates that littoral red muscle produces more force, per unit area, than pelagic red muscle. The non-significant differences between ecomorphs suggest there is little variability in muscle mechanics. Pelagic bluegills had significantly higher levels of both lactate dehydrogenase and citrate synthase activity in the myotomal muscle, as predicted by their superior swimming performance. This result supports the observation that pelagic fish are better steady and burst swimmers than littoral fish. Pelagic bluegills occupy open water habitats and have a wide array of fish predators which are likely selective pressure on steady/burst swimming performance and enzyme composition.
