The fish species present in Grand Teton National Park vary widely in shape, size and behavior. The mountain sucker feeds on algae. The cutthroat trout, named for the red slash under the lower jaw, feeds mainly on insects and smaller fish. The Utah chub lives in warm, shallow, slow-moving water. The mountain whitefish prefers cold, deep, fast-moving water. Despite their many differences, all fish are the primary food source for several species of birds, mammals, and other fish. The bald eagles depend on fish for their survival. Many other animals, including humans, consume fish as a secondary food source. Fish in turn control plant and insect populations. The well-being of fish worldwide is threatened by pollution, loss of habitat and overfishing.