COUGHLIN, D. J.; SPIECKER, A. T.; SCHIAVI, J. M. ; Widener University, Chester, PA: Aerobic Muscle Recruitment During Steady Swimming In Trout

Rainbow trout (Oncorhynchus mykiss) and brook trout (or charr, Salvelinus fontinalis) display different rostral-caudal patterns of power production by the red or aerobic muscle during steady swimming. The anterior muscle of rainbow trout produces much less power for swimming than the posterior, while in brook trout there is no variation in power output. To determine if red muscle recruitment is associated with anterior-posterior patterns of power production, electromyography (EMG) was used to record red muscle activity at three body positions across a range of swimming speeds in fish of each species. The initial recruitment of the anterior red muscle in swimming rainbow trout was predicted to lag behind (ie. occur at higher speeds) that of the posterior due to the variation in power production, but no variation in recruitment was expected for brook trout. EMG bursts from the red muscle of swimming fish were analyzed for tailbeat frequency, duty cycle (duration of bursts / tailbeat period) and burst intensity (integrated area of rectified bursts). Brook trout swam with higher tailbeat frequencies and longer values of duty cycle than rainbow trout. While there was no longitudinal difference in duty cycle of red muscle activity in brook trout, duty cycle was longer in anterior red muscle of rainbow trout. Burst intensity also differed significantly along the length of rainbow trout but not brook trout. In the former, burst intensity of anterior muscle was significantly less than the posterior at lower steady swimming speeds. The EMG data suggest that power production and muscle recruitment are related. In rainbow trout, where there is longitudinal variation in muscle power output, there are also significant rostral-caudal differences in red muscle recruitment.