The limitations of heart rate asa predictor of metabolic rate in fish

Although telemetered heart rate (f(H)) has been used as a physiological correlate to predict the metabolic rate (as oxygen consumption. VO2) of fish in the held, it is our contention that the method has not been validated adequately for fish. If f(H) in fish is to be used to estimate VO2 a single linear (or log-linear) relationship must be established for each species between the two variables which allows VO2 to be predicted accurately under ail environmentally relevant conditions. Our analyses of existing data indicate that while a good linear (or log-linear) relationship can be established between f(H) and VO2, the conditions under which the relationship applies may be quite restricted. Physiological states and environmental factors affect the relationship between f(H) and VO2 significantly such that several curves can exist for a single species. In addition, there are situations in which f(H) and VO2 do not covary in a significant manner. Ln some situations f(H) can vary over much of its physiological range while VO2 remains constant: in others VO2 may vary while f(H) is invariate. The theoretical basis for this variability is examined to explain why the use of telemetered f(H) in predicting VO2 of fish may be limited to certain specified applications. (C) 1996 The Fisheries Society of the British Isles