IMPORTANCE OF CONDITION FACTOR AND THE INFLUENCE OF WATER TEMPERATUREAND PHOTOPERIOD ON METAMORPHOSIS OF SEA LAMPREY, PETROMYZON-MARINUS

The incidence of metamorphosis of larval sea lamprey, Petromyzon marin us, was strongly affected by water temperature but not photoperiod. In a 1991 experiment, the development of metamorphosing animals in 13-de grees-C water was retarded about 1 mo relative to animals metamorphosi ng at 21-degrees-C and to a population from the Chippewa River, Michig an; the minimum length, weight, and condition factor (CF) of metamorph osing experimental animals were 117 mm, 2.8 g, and 1.50, respectively, and only 4% metamorphosed at 13-degrees-C and 18.9% at 21-degrees-C. In 1 992, with a population from the Great Chazy River, New York, 66% ot the animals at 13-degrees-C and 84% at 21-degrees-C metamorphosed. The higher incidence of metamorphosis in 1992 is partly related to the use of larvae that were larger than the minima established in 1991. W e predicted, using criteria defined below, that 74 and 72% of the anim als at 13 and 21-degrees-C, respectively, would metamorphose. Our pred ictions were consistent with observation at 13-degrees-C and for five of seven replicate tanks at 21-degrees-C. We suggest that a presumptiv e metamorphosing sea lamprey in landlocked populations should be at le ast 120 mm long, weigh 3.0 g, and have a CF greater-than-or-equal-to 1 .50 and that these criteria must he used in conjunction.