SHORT COMMUNICATION THE HEART RATE VARIABILITY SIGNAL IN RAINBOW

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. 19896). Regulation of the heart is usually studied by blocking components of the system by surgical or pharmaco-logical 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. The rainbow trout (Oncorhynchus mykiss=Salmo gairdneri) was chosen since it has been relatively well studied and has a dual cardiac innervation with both adrenergic and cholinergic elements (Gannon and Burnstock, 1969). Priede (1974) showed that heart rate variation in this species is abolished by section of the vagu