Methyl mercury bioaccumulation: A study of factors influencing uptake and elimination in fish

This research examined aspects of MeHg bioaccumulation in juvenile salmonids (Atlantic salmon, Salmo salar and rainbow trout, Oncorhynchus mykiss). The first aspect studied was the interaction of growth and MeHg bioaccumulation in short-term growth exposures. In two experiments using four different concentrations of dietary MeHg, it was found that rapidly growing fish actually accumulated Hg faster than slow growing fish. However, accumulation efficiency decreased inversely with ration; per unit of growth, slow growing fish accumulated MeHg with efficiencies approaching 100%, while for fish growing at 50 mg;A second aspect of this research examined the depuration of MeHg from juvenile rainbow trout in relation to dietary selenium. After short depuration times (25 days), fish fed selenium had lower body burdens than control fish. Elimination half lives for Hg were reduced from ca. ;Simple and accurate methods for measuring growth rates are important to fisheries biology and ecotoxicology. An ancillary aspect of this research on growth rate interactions with MeHg bioaccumulation in fish entailed the development of new growth estimators utilizing erythrocytes. The approach is based on the theory that erythropoiesis (the synthesis of erythrocytes) will be stimulated in order to support increased oxygen demand under conditions of rapid growth. In erythropoiesis, immature erythrocytes (reticulocytes) are released into circulation without hemoglobin, which is synthesized as the reticulocytes mature. Coincident with erythrocyte maturation, the hemoglobin synthetic apparatus will be initially active followed by senescence. Therefore, if erythropoiesis is stimulated, the net effect should be a rapid increase in the proportion of reticulocytes in the blood. This change should be measurable either by nucleic acid analysis (RNA concentrations or RNA/DNA ratios) or by reticulocyte enumeration on blood smears. In one experiment, RNA concentrations in whole blood, liver, and muscle, were analysed to compare the relative value of these parameters for estimating growth rates. A second experiment examined the use of microscopic enumeration of reticulocytes for estimating growth rates. In both experiments, fish were individually marked for determination of growth by increase in weight. In terms of RNA analysis, blood compared favourably with muscle and liver and was technically simpler to work with. Reticulocyte enumeration by microscope was technically simple and provided excellent results. Due to its low requirement for equipment, this technique for growth determination has great potential application for field situations.