During the egg stage of the lamprey’s life, it is most vulnerable to predators that prefer to eat fish eggs. Predation by other fish helps keep the lamprey numbers under control. When the lamprey has hatched from its egg into the larvae stage, it is limited to pools or backwater areas with a sand or sandy mud bottom. The young lampreys filter feed for food for around five to seven years until they are large enough to attach themselves to a host species. Spawning of this species of lamprey occurs from June to July when the animals are around seven to nine years old and migrate to tributaries to protect the young from predators, though most spawning activity has been observed in mid-June. During the mating process, one female would begin moving rocks from a suitable area for eggs; afterward she attaches herself to a rock while hopeful males attach to her and stroke her tail attempting to mate. The eggs are then covered with a rock, presumably to shade the young lampreys at birth and to keep any predators from devouring the young. After studying a number of male lampreys, researchers have discovered that the males have the ability to produce 15a-hydroxilated steroid, which some believe drives the male hormones for mating. The steroid hormome may explain why so many males gather around one female during the mating season. As with most lampreys, the chestnut lamprey (I. castaneus) only mates once during its entire life and dies shortly after. Adult lampreys put all their energy into ensuring a future for the next generation. With this species only producing eggs once in a lifetime and the potential predators, there is a small chance of an overpopulation of chestnut lampreys (I. castaneus).
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