The possibility of removing mercury from fish heavily contaminated by methyl mercury was examined in two series of rearing experiments using two marine species of fish: conger eel (Astroconger myriaster) and sea bream (Chrysophrys major).
In the first series, conger eel, caught from Kagoshima Bay, which had natural levels of mercury of 1.0ppm in the muscle tissue, 0.67ppm in the spleen, and 1.8ppm in the liver, were kept in plain sea water and fed with raw fish flesh for seven weeks. The mercury levels were reduced to one-half in 5 weeks for the muscle and spleen, and in 3 weeks for the liver.
In the second series, sea bream were fed for 7 weeks with pellets containing either methyl mercury or mercuric chloride at a level of 1.0ppm, and subsequently fed with either commercial pellet feed or pellets impregnated by a mixture of cysteine, pectin, and chitosan for another 7 weeks.
The mercury concentrations at the end of the first feeding period were 0.9ppm in the kidney and 0.25-0.4ppm in the muscle, liver, brain, and spleen. However, during the subsequent feeding period, the mercury level was reduced to a level less than 0.2ppm in every tissue examined, with best results in the group fed with the pellets supplemented by the mixture mentioned.
In the case of feeding with pellets containing mercuric chloride, the mercury level in any part hardly reached the level of 0.2ppm, even after a 7 weeks' period. This may suggest that mercury in this chemical form will excrete readily.