Accumulation of Mercury in Sea bream (Chrysophrys major) and Horse mackerel (Trachurus japonicus)

Abstract

Rate of accumulation of mercury in the different tissues of marine fish species was followed by setting two series of rearing experiments using sea bream (Chrysophrys major) and horse mackerel (Trachurus japonicus). In the first series, fish were fed with ground flesh of horse mackerel in the sea water added by mercuric chloride at the levels of 0.1ppm, 0.01ppm, and 0.001ppm. In the second one, fish were fed with pellets prepared from a variety of deep sea serranids (Malakichthys griseus) which accidentally gave a high concentration of methyl mercury; 1.4ppm. Both groups consisting 75 fish were held in aquaria with capacity of 3 tons of sea water for 91 days. In another series of experiment, the same number of fish were also fed by methyl mercury-containing pellets in the sea water added HgCl₂ at level of 0.1ppm.
In the first group of fish, mercury mostly accumulated in spleen, followed by brain, liver and muscle in the order of concentration. At the end of rearing period, mercury level of muscle was 0.3ppm and 3.0ppm, when they were held in sea water containing mercuric chloride of 0.01ppm and 0.1ppm, respectively. Almost negligible level of mercury in organic form was noticed in these tissues of fish after 13 weeks and this may suggest methylation of mercury hardly occur in these organs.
By oral intake of the pellets, mercury levels were much lower than those of branchial invasion. A level of 0.8ppm in the muscle and brain and 1.2ppm in the liver and spleen was detected respectively after 13 weeks of rearing. Mercury concentration in spleen was not so remarkable after oral feeding of methyl mercury.