Pollution and pelagic fish
Fish are through their gills continuously in direct contact with their environment. Unlike sea birds and marine mammals they can with these gills directly adsorb contaminants from their environment. Fish can therefore both be contaminated by eating and by direct uptake from the water. As they form the top of the food chain, large carnivorous fish will also experience problems from biomagnifying substances like methylmercury and organochlorine compounds.[1]
Heavy metals
Methylmercury can biomagnify to high values in large carnivorous fish. These fish are also more active, causing them to need more oxygen. To extract more oxygen, they have to pump more water through their gills, causing them also to adsorb more contaminants. Unlike marine mammals and (possibly) sea birds, fish can't demethylate methylmercury, nor can they excrete it efficiently. Therefore old carnivorous fish often contain very large amounts of methylmercury, making them unfit for human consumption.[2]
Organochlorine compounds
Organochlorine pesticides in the 1960s very often caused acute toxic effects in fish. When sprayed on agricultural areas near the coast, they tended to ended up in large doses in nearby bays, resulting in large fish mortalities. This for instance caused fisheries in the Laguna Madre, a bay in Texas, to collapse. This was caused by pesticides sprayed on nearby . [2]
Case studies
Case study 1:Effects of xenoestogens in eels
