Effects of temperature and body size on radiocaesium retention in brown trout, Salmo trutta

1. The elimination rate of radiocaesium in brown trout Salmo trutta L. was determined in the laboratory at four water temperatures (range 4.4–15.6°C). In the experiments three or four homogenous size-groups of fish (mean weights 23–496 g) were studied at each temperature. 2. The brown trout received acute oral doses of ¹³⁴Cs and were killed at intervals for radioactivity counting. The retention versus time curves were composed of two distinct exponential components. The long-lived component was quantitatively the most important for retention of radiocaesium. Elimination rate increased with increasing water temperature and decreased with increasing body weight. 3. The biological half-life of ¹³⁴Cs (T_b, days) was related to fresh body weight (W, g) and water temperature (t, °C) by the equation: T_b= 290 ×W°.¹⁷⁶× e-°.^106×t. The elimination rate of Cs could be predicted from weight-specific metabolic rate as given by Elliott's equations for brown trout.