Fred Herman, age 12, of St. Augustine, Fla., for his question:
IS THE LAMPREY A DESTRUCTIVE ANIMAL?
Lamprey is a fish with a long eel like body. Large sea lampreys rank as the most destructive to fishes. As adults, they descend to the sea and prey on large fishes.
Some sea lampreys that spawned in streams flowing to Lake Ontario once entered the Great Lakes through the Welland Canal. Later generations of these lampreys no longer descend to the sea, but prey on lake trout, whitefish and other large lake fishes.
By the late 1950s, the lampreys had killed most of the lake trout in the Great Lakes. Scientists tried to control the lampreys by putting electric weirs or fences across streams to prevent the lampreys from spawning. But the weirs were costly and difficult to maintain.
Researchers discovered that a chemical called TFM would kill lampreys but would not harm other fish in the rivers. The treatment of streams with this chemical caused a sharp decline in the number of lampreys by the mid 1960s. Conservationists then stocked the lakes with coho salmon, lake trout and other fishes.
Parasitic lampreys feed by attaching themselves to fishes, scraping a hole through the skin and sucking out blood and other body fluids. The adults of the nonparasitic lampreys do not eat. Their digestive organs degenerate and they live only until the spawning season. Then they spawn and die.
The lamprey is one of the least developed vertebrates, or animals with backbones. Unlike most other fishes, the lamprey has no bony skeleton. It has a back bone like notochord made of rubbery tissue called cartilage.
The lamprey has fins on its back but not on its sides. Its round mouth has no jaws but can create strong suction. Adults of some species develop horny teeth. Such an adult attaches itself to other fishes by sucking with its mouth and clamping with its teeth.
The lamprey's skin is smooth, shiny and scaleless.
Brook lampreys live in small streams throughout temperate parts of North America, Europe and Asia. They grow to be about eight inches long. Larger species live in rivers and lakes.
Sea lampreys, which may grow as much as three feet long, live in the North Atlantic and North Pacific oceans.
All lampreys are dull colored, ranging from light tan to mottled brown or bluish black. They do not have true bony teeth. The lamprey's teeth are horny developments that grow from the inner surface of the mouth.
Lampreys spawn in clear water streams. The male and female dig a shallow nest in the gravel or pebbles of the stream bottom. The female deposits the eggs in the nest.
Young lampreys are called ammocoetes. They are blind and toothless and look like worms. The ammocoetes live in the sand and mud of the stream bottom for several years. Then they change into adults, with eyes and teeth.