Extreme and Optimal Temperatures for Metamorphosis in Sea Lampreys

Abstract

The effect of water temperature on the incidence of metamorphosis in sea lampreys Petromyzon marinus was evaluated in a laboratory study to determine the optimal temperature and the temperature extremes for metamorphosis. The experiment began on June 4, 1996, and involved lampreys larger than 120 mm and 3.0 g in size. The incidence of metamorphosis was 0% at 9°C, 80% at 21°C, and 58% at 25°C. By August, the median stage of metamorphic development for each temperature was stage 4 at 17°C and 21°C, stage 3 at 25°C, and stage 2 at 13°C. Based on the incidence of metamorphosis and the rate of development, we conclude that 21°C is near optimum for metamorphosis of sea lampreys and that the lower thermal limit for metamorphosis in sea lampreys is between 9°C and 13°C. An upper thermal limit could not be determined from our data. Our results support the hypothesis that spring temperature is an important cue for metamorphosis in lampreys, and they also demonstrate that temperature exposure in the month immediately prior to metamorphosis (June) is critical for normal commencement of this event.