ABSTRACT
Records of heart rate often show short-term variation in beat-to-beat interval which can be plotted as a heart rate variability signal (HRVS). It has been suggested that, in mammals, analysis of the HRVS can be used as a quantitative means of investigating control of cardiac function (McDonald, 1980). An HRVS can be recognised in the electrocardiograms (ECGs) of teleost fishes (Armstrong et al. 1989a) and these signals have been recorded by telemetry from free-living fish in their natural environment (Armstrong et al. 1989b). Regulation of the heart is usually studied by blocking components of the system by surgical or pharmacological intervention or using in vitro isolated preparations (Farrel, 1984). Analysis of the HRVS may provide a unique insight into the function of the intact system and should be applicable to free-swimming fish in their natural environment.
