LONG-TERM INFLUENCE OF WATER TEMPERATURE, PHOTOPERIOD, AND FOOD-DEPRIVATION ON METAMORPHOSIS OF SEA LAMPREY, PETROMYZON-MARINUS

After 11 mo in the laboratory, significantly more sea lamprey, Petromy zon marinus, larvae from the Chippewa River, Michigan, metamorphosed i n an ambient temperature regime (3 +/- 2 animals.tank(-1)) compared wi th a fixed 21 degrees C temperature (0 animals); photoperiod and food deprivation did not have detectable effects on the incidence of metamo rphosis. Metamorphosing animals in our laboratory study were significa ntly smaller in size (length and weight) and had a lower condition fac tor (CF) than animals from the same population that metamorphosed a ye ar earlier under field and shorter term laboratory conditions. We also predicted, using criteria of 120 mm, 3.0 g, and a CF of 1.50, that 12 and 14% of the animals in the ambient and fixed temperature regimes, respectively, would metamorphose. Our prediction for the ambient tempe rature did not differ significantly from observed (11%). We suggest th at larvae in landlocked populations of sea lamprey that are at least 1 20 mm long, weigh 3.0 g, and have a CF of 1.50 or greater in the fall can be predicted to metamorphose the following summer. Furthermore, ou r data show that low temperature during the winter followed by rising temperature in the spring is the primary environmental cue initiating metamorphosis in sea lamprey.