The uptake of radioactive phosphorus by brown trout ( Salmo trutta L.) from water and food

Brown trout were exposed to 32P in their tank water (7.4 Bq l −1) and the uptake to muscle followed over 6 weeks. A steady-state concentration factor (C ss) of 1.7 and a biological half-time for clearance ( t b1 2 ) of 45 days were calculated from the results. The low C ss indicates that uptake from water is not a major route of 32P accumulation in these fish. Brown trout were given a single 32P-spiked meal, and the uptake and clearance in muscle, liver and blood followed over 6 weeks. Assimilation of the isotope by these organs was low, the maximum activity in whole muscle reaching only 0.2–0.4% of that in the meal with lower values in the other two organs. There was no appreciable clearance of 32P from muscle during the experiment. The slow clearance of 32P after uptake from water and lack of any clearance after uptake from food indicates that the C ss for this isotope following uptake by either route is likely to depend on radioactive decay rather than intake rate and physiological clearance.