Lampreys and Hagfishes

Marine fishers sometimes find hagfishes to be a minor nuisance because they swim into deep-set nets and eat some of the catch. They are extremely messy and unpleasant to remove from nets, because of the copious, thick, sticky slime that covers their body.

The sea lamprey (Petromyzon marinus) is an important parasite of economically important species of fish in the Great Lakes of North America. This species was probably native to Lake Ontario, but it spread to the other Great Lakes after the construction of the Welland Canal in 1829 allowed the sea lamprey to get around Niagara Falls, which had been an insurmountable barrier to its movement up-river. The sea lamprey was similarly able to colonize Lake Champlain after a transportation canal was built to link that large water body to the sea. The sea lamprey now occurs in all the Great Lakes and in other large lakes in North America, where it parasitizes all of the larger species of fish and greatly reduces their productivity. The lake trout (Salvelinus namaycush) was virtually eliminated from some lakes by the sea lamprey, and probably would have been extirpated if not for the release of young trout raised in hatcheries.

The deleterious effects of the sea lamprey are now controlled to a significant degree by the treatment of its spawning streams with a larvicidal chemical (TFM, or 3-trifluoromethyl-4-nitrophenol) that is applied to the water, killing the ammocoetes. However, TFM cannot be applied to all of the breeding habitats of the sea lamprey, and this parasite continues to cause important damage to commercial and sport fisheries, especially on the Great Lakes.