Parasites are emerging as important sentinels of ecosystem health because parasites only thrive in habitats with the proper suite of intermediate hosts, the correct physical and chemical conditions, and conducive physiology of the fish host. Recent research in a variety of disciplines suggests that parasites may in fact be as important as predation and competition in structuring animal populations. Fish parasites have long been used as natural tags in delineating stocks, because the fish need only be captured once.
To aid fisheries researchers, a recent paper "Parasites of the fishes of Alaska and surrounding waters" synthesizes the 135 published records on the parasites of the fishes of Alaska, the Bering Sea, and the Gulf of Alaska. Although 967 parasite/host combinations are described for Alaska waters and 255 parasite species have been recorded from Alaska fishes, parasites have only been noted from 89 of the more than 600 species of fish thought to inhabit the area.
The parasite fauna of only a few fish species in Alaska can be characterized as well described: Pacific halibut (53 known parasite species), sockeye salmon (47 species), Pacific ocean perch (35 species), walleye pollock (34 species), and pink salmon and rougheye rockfish (32 species each). Protozoan parasites, which hold promise as natural tags, have been largely ignored in parasite surveys with only 20 genera having been described from 17 species of fish.
