Meeting Abstract
In vitro studies have shown that temperature can directly affect muscle mechanics. However, as climate changes, it is increasingly important to see how ectotherms physiology is impacted. Here we investigate in vivo muscle mechanics under varying water temperatures during steady swimming in largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). Fish were collected in central Illinois streams and housed at 20°C until tested in a recirculating flow tank swimming steadily at 2 body length (BL)/sec at three different temperatures: 16°C, 20°C and 22°C. To perform intramuscular electromyography, bipolar electrodes were inserted through the skin into epaxial white muscle at below the dorsal fin (axial, 0.5BL) and epaxial red muscle both below the dorsal fin (axial, 0.5BL) and closer to the tail (caudal, 0.75BL). Electromyographic recordings were analyzed for magnitude, frequency, onset, offset, duration and duty cycle. We found that in largemouth bass white muscle suffers a phase shift with increased temperature and is recruited concurrently with red muscle. At higher temperatures, bass also have greater contraction magnitude in both white axial and red caudal muscles, but not in axial red muscle; while contraction frequency decreases. In contrast, the main differences in in vivo muscle mechanics in bluegill were increased duty cycles of caudal and axial red muscles at higher temperatures, although caudal red muscle appears to contribute the most to power output. This study reveals that in vivo muscle mechanics in centrarchids are altered with changes in water temperature. In bass, additional recruitment of white muscle at higher temperatures can lead to early fatigue and have strong metabolic impacts. Bluegill appear to use a different strategy by altering the contraction dynamics of red muscle, which can directly increase energy expenditure.
