Sea Lamprey are unusual in having a complex life cycle, whereas most fish have a simple life cycle.
1.) Sea lampreys go through an extended larval phase before metamorphosing into the bloodsucking parasitic phase. Each summer and fall there is one group of parasitic sea lampreys actively feeding in the Great Lakes.
2.) The next spring, that group leaves the lake and migrates into tributary streams where they must build nests in clean gravel with flowing water.
3.) Each female spawns an average of 60 to 70 thousand eggs.
3.) Each female spawns an average of 60 to 70 thousand eggs.
4.) After hatching, the larvae drift downstream to areas with slower currents and sand/silt bottoms. There, they establish permanent burrows and enter a larval stage varying in duration from 3 to 10-or even more years.
5.) Larvae lack eyes and the oral disc. Living concealed in their burrows, they are harmless and filter microscopic material from the water for food. When they reach lengths of 120 mm or more, some individuals begin metamorphosis in mid-summer.
6.) During metamorphosis they develop eyes, the oral disc, and changes in their kidneys that (in their native range) would allow them to enter the salt water of the Atlantic Ocean. That fall or the following spring, they instead enter the Great Lakes to feed parasitically on fish that summer and fall, and mature and spawn the next spring—completing their life cycle. Sea lampreys only spawn once and then die after spawning.
