The research, conducted in the Bay of Biscay west of France, also discovered the first case of a deep water fish species with an "intersex" condition, a blend of male and female sex organs. The sampling was done in an area with no apparent point-source pollution, and appears to reflect general ocean conditions.
The findings have been published in Marine Environmental Research, by scientists from Oregon State University; the Centre for Environment, Fisheries and Aquaculture Science in the United Kingdom; and other agencies. It was supported by the European Union.
The research is of particular interest, OSU researchers said, when contrasted to other studies done several years ago in national parks of the American West, which also found significant pollution and fish health impacts, including male fish that had been "feminized" and developed eggs.
"In areas ranging from pristine, high mountain lakes of the United States to ocean waters off the coasts of France and Spain, we've now found evidence of possible human-caused pollution that's bad enough to have pathological impacts on fish," said Michael Kent, a professor of microbiology in the OSU College of Science, co-author on both these research projects and an international expert on fish disease.
"Deep in the ocean one might have thought that the level of contamination and its biological impact would be less," Mr Kent said. "That may not be the case. The pathological changes we're seeing are clearly the type associated with exposure to toxins and carcinogens."
However, linking these changes in the deep water fish to pollution is preliminary at this time, the researchers said, because these same changes may also be caused by naturally-occurring compounds. Follow up chemical analyses would provide more conclusive links with the pathological changes and man's activity, they said.
Few, if any health surveys of this type have been done on the fish living on the continental slopes, the researchers said. Most past studies have looked only at their parasite fauna, not more internal biological problems such as liver damage. The issues are important, however, since there's growing interest in these areas as a fisheries resource, as other fisheries on the shallower continental shelf become depleted.
As the sea deepens along these continental slopes, it's been known that it can act as a sink for heavy metal contaminants such as mercury, cadmium and lead, and organic contaminants such as PCBs and pesticides. Some of the "intersex" fish that have been discovered elsewhere are also believed to have mutated sex organs caused by "endocrine disrupting chemicals" that can mimic estrogens.
In this study, the health concerns identified were found in black scabbardfish, orange roughy, greater forkbeard and other less-well-known species, and included a wide range of degenerative and inflammatory lesions that indicate a host response to pathogens, as well as natural cell turnover. The fish that live in these deep water, sloping regions usually grow slowly, live near the seafloor, and mature at a relatively old age. Some can live to be 100 years old.
Partly because of that longevity, the fish have the capacity to bioaccumulate toxicants, which the researchers said in their report "may be a significant human health issue if those species are destined for human consumption."
Organic pollutants in such species may be 10-17 times higher than those found in fish from the continental shelf, the study noted, with the highest level of contaminants in the deepest-dwelling fish.
However, most of those contaminants migrate to the liver and gonads of such fish, which would make their muscle tissue comparatively less toxic, and "generally not high enough for human health concern," the researchers wrote.
In the previous research done in the American West, scientists found toxic contamination from pesticides, the burning of fossil fuels, agriculture, industrial operations and other sources, which primarily found their way into high mountain lakes through air pollution. Pesticide pollution, in particular, was pervasive.
Together, the two studies suggest that fish from some of the most remote parts of the planet, from high mountains to deep ocean, may be impacted by toxicants, Mr Kent said.