Development of an acoustic telemetry tag for monitoring electromyograms infree-swimming fish

We report the development of an acoustic telemetry tag used to monitor elec tromyograms (EMGs) remotely from free-swimming marine fish. The device desc ribed amplifies and filters the EMG and then converts the electrical wavefo rm into a frequency-modulated acoustic signal that is transmitted through w ater. The signal is then received, demodulated and recorded by the receivin g system. The EMG tag described has been tested on a range of species, incl uding toadfish Opsanus tau, spiny dogfish Squalus acanthias, yellowfin tuna Thunnus albacares and eastern Pacific bonito Sarda chiliensis, in differen t tank environments. In certain tanks the fidelity with which the system re plicates the EMG is sufficient to quantify accurately the onset, offset, du ration, the integrated area under the absolute value of the signal and the number of signal zero crossings. This EMG tag will expand the scope of ques tions that can be addressed about the behavior and physiology of free-swimm ing fish.