Just like other lampreys, sea lampreys have a monstrous suction mouth with rows of small grating teeth. Using these teeth, they clamp onto large fish to suck their blood. This is necessary for survival. They attach themselves so tightly that the victims are not usually able to shake them off, despite the suffering they incur from these parasitic fish. The wounds made by the lampreys can cause death in the victims. Sea lampreys are born in fresh water. They live in the mud as larva for several years. Only after maturing do they move to the sea, only returning to the river to lay eggs.