There are four stages in the life cycle of sea lampreys, which usually spans 18 months but can last as long as 5 years. The first of these stages is the spawning phase, which occurs during spring and early summer. From April to June, sea lampreys search freshwater rivers and streams, seeking an ideal location in which to construct a nest and lay their eggs. Once the area is selected, male sea lampreys construct a nest, often moving rocks to create a large indenture or depression in the river or lake bed. A female then lays 30,000 to 100,000 eggs, which the male externally fertilizes. Both male and female adult sea lampreys float away and die soon after spawning. Unique to this phase is the disintegration of the digestive system; adult sea lampreys cannot feed while spawning. During the second phase, fertilized eggs settle into the sand or gravel and begin to grow. Within a few weeks, the eggs hatch and the larvae burrow further into the sand or gravel. Larvae filter-feed on algae and other aquatic organic matter. This larval phase can last for more than three years. In the third phase, known as transformation, larvae metamorphose into adult sea lampreys. During this phase sea lampreys develop a mouth, teeth and eyes. They also migrate to larger bodies of water, such as oceans or freshwater systems like the Great Lakes. Sea lampreys remain in this habitat for 12 to 18 months as a mature adult and begin to feed, attaching themselves to fish. This is known as the parasitic phase, during which sexual reproductive organs develop.
Development - Life Cycle: metamorphosis ; indeterminate growth