Influence of body size on the uptake or depuration of ¹³⁷Cs originating from feed in three salmonid species

We conducted feeding experiments under controlled conditions and assessed the trophic transfer of radiocesium in three salmonid species (Oncorhynchus nerka, O. masou, and Salmo trutta) with different body sizes. The assimilation efficiency of ¹³⁷Cs from the ¹³⁷Cs-containing feed until day 252 was clearly higher in small-sized than in large-sized fish across all species. After the diet was changed from R pellets (containing ¹³⁷Cs) to non-contaminated pellets, the ¹³⁷Cs excretion coefficient for the excretion period (days 56–252) was clearly higher in small-sized than in large-sized fish across all species. The effective half-lives of ¹³⁷Cs in the small-sized and large-sized fish of each species ranged from 34.5 to 40.3 days and from 86.2 to 100.8 days, respectively. The steady-state ¹³⁷Cs concentrations for the uptake period (days 0–252), as estimated by a model, were higher in large-sized than in small-sized fish across all species. Therefore, differences in body size may partly contribute to the varying ¹³⁷Cs contamination levels observed in the muscle of the fish.