Induction of metamorphosis in landlocked sea lampreys, Petromyzon marinus

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Abstract
Landlocked larval sea lampreys (Petromyzon marinus) in three size‐groups were treated with two concentrations of potassium perchlorate (0.01 and 0.05% KC104; 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 size‐groups with both concentrations of KC1O4 but not in control animals. Size‐group was the only factor that significantly influenced (P < 0.05) the incidence of metamorphosis, which was 22% (13/60) in the 65–95 mm group, 52% (31/60) in animals 110–119 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 (±SEM) CFs of metamorphosing animals in the three size‐groups were 1.22 ± 0.04 (65–95mm), 1.25 ± 0.02 (110–119 mm), and and 1.27 ± 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 KC1O4. 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.

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