Estimating the Active Metabolic Rate (AMR) in Fish Based on Tail Beat Frequency (TBF) and Body Mass JAN OHLBERGER 1Ã , GEORG STAAKS 1 , AND FRANZ HO ¨ LKER 1,2 1 Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany 2 European Commission, DG Joint Research Centre, Institute for the Protection and Security of the Citizen, AGRIFISH Unit, Ispra, Italy ABSTRACT Tail beat frequency (TBF) was measured for carp (Cyprinus carpio) and roach (Rutilus rutilus), during steady swimming at five different speeds and for fish of various body masses. A multiple stepwise linear regression analysis resulted in models for the prediction of TBFs depending on swimming speed as an independent variable. Speed explained 72 and 86% of the variance in TBF for carp and roach, respectively. By using these data to predict TBF from speed and substituting values into a model from a previous study that predicts active metabolic rates (AMR) from body mass and swimming speed, we can calculate AMR from only fish mass and TBF. Thus, the derived models can be used to estimate the AMR in fish by measuring TBFs in the field using biotelemetry. The approach presented here is a useful and relatively simple tool for estimating the activity metabolism in free-swimming fish. In future studies this method should be applied to a larger and more representative sample size to test the applicability and the validity for a broader range of species. J. Exp. Zool. 307A:296–300, 2007. r 2007 Wiley-Liss, Inc. How to cite this article: Ohlberger J, Staaks G, Ho ¨lker F. 2007. Estimating the active metabolic rate (AMR) in fish based on tail beat frequency (TBF) and body mass. J. Exp. Zool. 307A:296–300. The energetics and activity of free-swimming fish is of great interest to ecologists, because activity costs in fish are directly linked to food capture, predator avoidance, growth rate, repro- duction and habitat shifts (Videler, ’93; Webb, ’94). As swimming activity accounts for the largest portion of the energy budget of a fish (Jobling, ’94; Ho ¨lker and Breckling, 2002), accurate estimates of swimming costs are required for developing bioenergetics models in ecological fish studies. The actual metabolism of free-ranging fish in the wild cannot be measured directly, because respiration measurements are not feasible under these conditions. Thus, metabolic rates of fishes in the field have to be determined based on labora- tory measurements of the energy consumption of the fish. Different methods have been proposed to esti- mate the metabolic rate of fish in the field, for example by doubling the standard metabolic rate (Winberg, ’56) or by including spontaneous activ- ity in laboratory tests of fish swimming (Jobling, ’82). However, these methods only provide rough estimates, as the actual activity level of the fish cannot be considered. The actual activity metabo- lism in free-swimming fish has to be assessed based on laboratory-derived models combined with direct measurements of fish activity by telemetric field studies. Biotelemetry represents a precise method to link field metabolic rates to laboratory-derived esti- mates of the energy expenditure. Radio or ultra- sonic transmitters can be used to estimate field rates by measuring aspects of fish physiology such as heart rate, axial muscle activity, and ventilation rate or tail beat frequency (TBF) as indices of locomotor activity (Cooke et al., 2004a). TBF has proved to be an accurate indicator of the swim- ming activity in carangiform and subcarangiform swimmers (Bainbridge, ’58; Hunter and Zweifel, ’71; Steinhausen et al., 2005). Electromyogram (EMG) locomotory activity telemetry seems to be Published online 15 March 2007 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/jez.384. Received 5 January 2007; Accepted 9 February 2007 Ã Correspondence to: Jan Ohlberger, Leibniz-Institute of Fresh- water Ecology and Inland Fisheries, 12587 Berlin, Germany. E-mail: Ohlberger@igb-berlin.de r 2007 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY 307A:296–300 (2007)