Fishes concentrate mercury in their bodies, often in the form of methyl mercury, a highly toxic organic compound of mercury. The mercury is absorbed, usually as methylmercury, by algae at the start of the food chain. It gets magnified to about 0.01 ppm in the herring, tuna etc. The same fishes when consumed by the human get more concentration of mercury. In Sharks, the mercury gets accumulated to the extent of 1 ppm.
The disease was searched in the seaside town of Minimata, in Japan in late 1950s when a strange behaviour in animals was seen. The abnormal behaviour was seen in the Cats, Birds and also in Humans. Investigations found that a petrochemical company had been discharging mercury waste into the sea. Around 5,000 people were killed and perhaps 50,000 have been to some extent poisoned by mercury. Thus, this disease got famous as Minimata disease.