Biology of the sea lamprey in its parasitic phase

The investigations conducted on sea lampreys in aquariums were concerned with the duration of the parasitic phase of life, feeding, growth, and the interrelations between predator and host fish. Observations on lampreys reared from metamorphasis to maturity were made at the Fish and Wildlife Service Laboratory at Hammond Bay, Michigan.

Most of the experimental lampreys were mature and ripe after 14 to 18 months of parasitic life. They exhibited signs of irreversible physical degeneration which precedes death. Three specimens were immature at 14, 18, and 26 months in aquariums, thus indicating that under certain conditions, lampreys may extend their parasitic phase.

It is estimated that the average fish-kill by a wild lamprey exceeds and could be approximately double the 18.5 pounds of fish killed by a laboratory lamprey. The rate and extent of fish destruction depended on the size, sex, and stage in the parasitic phase of the lampreys, and on the species and size of the fish. There was an increase in the number of fish killed as the lampreys grew, and the fish were killed more quickly. Attacks made by experimental lampreys at any stage of their parasitic phase up to full maturity, and on any part of a prey fish except fins, usually resulted in death to the host. Some fish which survived lamprey attacks succumbed to fungus infections of the wounds. A small number of trout recovered from attacks, and their wounds healed.