Population and Energy Dynamics of Trout Salmo trutta in a Small Danish Stream

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Abstract
(1) Data on population size, growth, production and food consumption of trout, Salmo trutta, in a small Danish stream were obtained from March 1974 to April 1976. Annual production in the 2 years was 88.9 (95% C.L. 82.6-97.4) and 65.8 kJ m-2 (95% C.L. 60.8-73.1), respectively, and the maximum rate of production coincided with the period of maximum growth rates. (2) Food consumption was estimated from: (a) equations based on observed growth rates and experimental data on growth and food consumption (Cactual) and (b) Winberg''s balanced equation based on approximation of the standard metabolic rate (CWinII). The equation relating standard metabolic rate of body weight, RS = aWk, was determined from experiments on oxygen consumption at different temperatures. The k estimate of 0.93 differed significantly from the general value of 0.76 suggested by Winberg but was not different from published values from brown trout. For comparative purposes the food cohnsumption, CWinII1 and CWinII2, based on k = 0.76, respectively, was estimated. The annual food consumption in each of the 2 years was Cactual; 479.2 (range 448.3-521.9) and 369.8 kJ m-2 (range 343.5-406.8), CWinII1: 784.2 (range 738.6-851.6) and 609.4 kJ m-2 (range 574.7-663.9) and CWinII2: 619.6 (range 579.7-674.6) and 481.1 kJ m-2(range 447.7-529.0). (3)The Cactual, CWinII1 and CWinII2 values differed significantly. It is emphasized that the assumptions inherent in Winberg''s balanced equation, i.e. (a) weight exponent k = 0.76, (b) assimilation efficiency, A = 80% and (c) the metabolic rate of fish in nature is twice the level of standard metabolism, have to be tested for any actual study before the balanced equation is used. However, observed growth rates and equations based on feeding experiments provide an adequate method for studying energy requirements of brown trout populations.