THE USE OF A PERFUSED, WHOLE-BODY PREPARATION TO MEASURE THE BRANCHIAL AND INTESTINAL INFLUX OF 137-CESIUM IN THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The branchial and intestinal influx of caesium (Cs) in the rainbow tro ut (Oncorhynchus mykiss) were measured using a perfused whole-body pre paration. The branchial influx of Cs was small, 0.31 mumoles kg-1 h-1 at an external concentration of 1 mM. Branchial Cs influx was saturabl e, with a K(m) of 1.92 mm and a J(max) of 1-05 mumoles kg-1 h-1. Intes tinal Cs influx was not saturable, but was directly proportional to th e mucosal Cs concentration. Intestinal Cs influx was approximately 10- 40 times greater than branchial Cs influx over a wide range of externa l Cs concentrations. These results are discussed with respect to mecha nisms of Cs uptake and to the relative accumulation of radiocaesium fr om water and food in the environment.