ARE MUSCLE-FIBERS WITHIN FISH MYOTOMES ACTIVATED SYNCHRONOUSLY - PATTERNS OF RECRUITMENT WITHIN DEEP MYOMERIC MUSCULATURE DURING SWIMMING IN LARGEMOUTH BASS

The myomeric axial musculature of fish has a complex three-dimensional morphology, yet within-myomere motor patterns have not been examined to determine whether all portions of each myomere are activated synchr onously during locomotion, To gain insight into recruitment patterns i n the deep myomeric musculature of fish, we implanted a series of fine -wire electrodes arranged in a vertical row of six electrodes and a lo ngitudinal row of three electrodes on both the left and right sides of each of five largemouth bass (Micropter us salmoides), After recordin g electromyograms (EMGs) during the burst-and-glide swimming of each f ish, post-mortem dissections and X-rays determined the location of ele ctrodes with respect to (1) the longitudinal position (by counting the underlying vertebrae), (2) the position of the myomere containing the (3) the portion within each myomere an electrode, Because of the conv oluted overlapping shape of the myomeres, electrodes within the vertic al row of sites could be located in any one of six different myomeres, Thus, we compared muscle activity for locations with a constant longi tudinal position and differing myomeric position (vertical row) and am ong sites with both variable longitudinal and myomeric positions, We d etected significant heterogeneity in EMG onset times for sites within the vertical row of electrodes; however, the durations of the EMGs fro m different sites were similar, EMG onset times at more posterior long itudinal positions preceded those of more anterior longitudinal positi ons when electrodes of the latter site were within a more posterior my omere, Thus, the timing of EMGs was consistent with the posterior prop agation of muscle activity via the sequential activation of myomeres r ather than the simultaneous activation of all contractile tissue withi n the longitudinal span of a single vertebra, In addition, extreme epa xial and hypaxial portions of myomeres showed distinct activity patter ns which did not necessarily correlate with activity in the central my omeric fibers nearer the horizontal septum.