Effects of Temperature on Metamorphosis and the Age and Length at Metamorphosis in Sea Lamprey (Petromyzon marinus) in the Great Lakes

Abstract

Sea lamprey (Petromyzon marinus) ammocoetes of known age were confined in three locations to determine the effects of temperature on the incidence of metamorphosis. Sixty ammocoetes were held in each of Lake Superior, the Big Garlic River, and in an aquarium at room temperature for each of 4 yr. The highest incidence of metamorphosis (75–100%) occurred at 20–21 °C (aquarium), an intermediate rate (46–76%) at 14–16 °C (Big Garlic River), and the lowest (5–10%) at 7–11 °C (Lake Superior). Density appeared to be the dominant factor in regulating the length of larval and transformed sea lampreys. Mean lengths of larval and transformed sea lampreys increased markedly after stream treatments with selective lampricides. Prediction of lengths at which metamorphosis occurs in re-established populations of sea lampreys is uncertain because of variability in growth rates. Initial metamorphosis in a year-class is dependent on growth rates of ammocoetes. Because of wide variation in growth rates, metamorphosis may begin at age III among fast-growing populations and not until age VII among slow-growing populations.Key words: Petromyzon marinus, sea lamprey; metamorphosis, age, length, Great Lakes