Dynamics of dietary methylmercury in rainbow trout, Salmo gairdneri

Rainbow trout, Salmo gairdneri, were fed diets containing 0, 25, 45, 75 or 95 mg Hg · kg −1 methylmercury for 84 days at meal sizes of I and 2% · day −1 and to satiation. Uptake and depuration of methylmercury was followed in fish fed fixed rations by feeding some of these fish diets containing 203Hg-labeled methylmercury. Appetite, apparent digestibility of ration and growth decreased in fish fed diets containing added methyl-mercury. Whole body mercury concentrations of trout fed diets containing added methylmercury increased throughout the first 56 days of feeding, then generally stabilized from 56–85 days. The total amount of mercury in the fish, however, increased throughout the 84 days. Trout generally assimilated 70–80% of the labelled methylmercury they were fed. Among fish fed the 75 ing Hg · kg −1 diet for 9 wk, assimilation decreased to < 50%, indicating either a saturation of uptake or an induction of a specific block to methylmercury assimilation. Labeled methylmercury was depurated faster in fish fed the higher meal size. Methylmercury depuration in rainbow trout would thus seem related to metabolic rate. Trout fed diets containing added methylmercury depurated labeled methylmercury more rapidly than fish fed diets without added methyl-mercury, suggesting that methylmercury depuration may be induced by continued exposure to the compound.