ELECTROMYOGRAMS FROM RADIOTELEMETRY AS INDICATORS OF REPRODUCTIVE ACTIVITY IN LAKE TROUT

One male and one female lake trout, Salvelinus namaycush, were held in a laboratory tank simulating a natural spawning environment. Their be haviour during their reproductive period was videotaped each day for 2 h at dusk. The fish activities were classified into seven types: rest ing, casual swimming, side-thrusting, chase, chase-nudge, body alignme nt, shuddering. As the reproductive period progressed the fish became more generally active with a marked increase in interactive behaviours such as pursuit of the female by the male (chasing, chasing-nudging). Around spawning time, shuddering and body alignment activity reached a peak. Each fish was equipped with an internally implanted radiotelem etry package able to detect and transmit continuously over the course of each day signals that reflect production of the electromyograms (EM Gs) that accompany fish axial muscle activity (high muscular activity gives low pulse interval times in milliseconds). The lowest EMG pulse intervals corresponded with what, from the video records, appeared to be the time of highest physical activity during the reproductive perio d-viz. that associated with spawning activity during dusk. Other times during the diel cycles over the reproductive period, except for times of roughly similar duration during early morning (which may also be r eflections of spawning) showed considerably lower muscular activity. I t is concluded that transmitted EMG records could probably be used as indicators of spawning activity of lake trout in at least some of thos e places in the field where they cannot normally be located by visual means. (C) 1996 The Fisheries Society of the British Isles