Pollution and pelagic fish

Fish are through their gills continuously in direct contact with their environment. Unlike sea birds and marine mammals they can therefore directly adsorb contaminants from their environment. Fish can therefore both be contaminated by eating and by direct uptake from the water. Large carnivorous fish will also experience problems from biomagnifying substances like methylmercury and organochlorine compounds.

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.

Organochlorine compounds

Chronic PCB contamination might affect the breading success of benthic fishes. The starry flounder population in the San Fransisco Bay displayed reduced breading success in the 1980's. Although the San Francisco bay had a relatively low PCB content, the eggs of the flounders displayed elevated PCB levels. This might lead to reduced number of eggs which hatch, bu also to reduced survivel of the juveniles, which might suffer from growth anomalies. Organochlorine pesticides in the 1960s very often caused acute toxic effects in fish. This for instance caused fisheries in the Laguna Madre, a bay in Texas, to collapse. This was caused by pesticides sprayed on nearby agricultural areas.

Case studies

Case study 1:Effects of xenoestogens in eels