09/11/2012 05:22 pm ET

12 Worst Invasive Fish On Earth

They lurk beneath the water, unseen until snagged by a fisherman or researcher. Some of these fishy intruders have traveled entire continents to their new habitats, relocated by accident in a manner that just would not have been possible until human beings began crisscrossing the globe at will. A number of these fish, on the other hand, were purposefully introduced to provide food and sport, or even to fight disease. Others are escaped pets, chancing their way in the great blue yonder.

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