Abstract
Landlocked larval sea lampreys (Petromyzon marinus) in three sizeโgroups were treated with two concentrations of potassium perchlorate (0.01 and 0.05% KC10~4~; a goitrogen) for 117 days during the winter to determine if metamorphosis can be induced at a time when it will not occur spontaneously and whether a minimum size (length and weight) and physiological condition, measured as a condition factor (CF), are necessary for induction to occur. Metamorphosis was induced in all sizeโgroups with both concentrations of KC1O~4~ but not in control animals. Sizeโgroup was the only factor that significantly influenced (P < 0.05) the incidence of metamorphosis, which was 22% (13/60) in the 65โ95 mm group, 52% (31/60) in animals 110โ119 mm long, and 98% (59/60) in animals >130 mm long. Metamorphosing animals were significantly larger (P < 0.05) in size (length and weight) and had significantly higher (P < 0.05) CFs than unmetamorphosed larvae. The mean (ยฑSEM) CFs of metamorphosing animals in the three sizeโgroups were 1.22 ยฑ 0.04 (65โ95mm), 1.25 ยฑ 0.02 (110โ119 mm), and and 1.27 ยฑ 0.02 (>130 mm) and the smallest animal to metamorphose was 84 mm and 0.71 g in size. Minimum size and CF criteria for spontaneous metamorphosis (120 mm, 3.0 g, 1.50 CF) in landlocked sea lampreys are not necessary prerequisites for inducing metamorphosis using KC1O~4~. The experimental production of metamorphosis in sea lampreys of various sizes creates a valuable tool for studying hormonal and genetic regulation of this developmental strategy in a vertebrate of ancient lineage. ยฉ 1993 WileyโLiss, Inc.