Significance of subcellular metal distribution in prey in influencing the trophic transfer of metals in a marine fish

We investigated how the subcellular metal distribution in prey affects metal dietary assimilation in a marine fish, the grunt Terapon jarbua. The assimilation efficiency (AE) of metals (Cd, Se, and Zn) in the grunt varied by prey, which included copepods, barnacles, clams, mussels, and fish viscera. The AEs were 3-9% for Cd, 13-36% for Se, and 2-52% for Zn. The AEs of Se and Zn were significantly correlated with the subcellular Se and Zn distributions in the prey, suggesting that the subcellular forms of Se and Zn in the fish's diet affected assimilation. Further experiments determined AEs using purified subcellular fractions of copepods and mussels as fish diets. AEs were higher in the grunts fed the heat-stable protein fraction or the heat-sensitive protein fraction than in those fed insoluble fractions. AEs were comparable in fish fed purified subcellular fractions from different prey, further indicating the importance of subcellular metal distribution in metal assimilation. AEs of Se and Zn but not Cd were significantly dependent on the ingestion rate of fish and gut passage times for metals, suggesting that fish had different digestive strategies to handle essential and nonessential elements. Assimilation of metals by marine fish is determined both by the subcellular metal distribution in the prey and by the feeding process of the fish.