Ontogenetic metamorphosis and extreme sexual dimorphism in lumpsuckers: Eumicrotremus asperrimus, Cyclopteropsis bergi and Cyclopteropsis lindbergi, may be synonymous.

ABSTRACT

Cyclopterids were hatched from egg batches that were laid in two empty buccinid snail shells collected from a depth of 340 m in the Sea of Japan. Larvae were reared to identify species and to describe the morphological changes associated with metamorphosis. The fin rays of all fins were mostly complete and the pelvic fins were modified to form suckers, or adhesive discs, at the time of hatching. Juveniles immediately attached themselves to the bottom and there was no planktonic stage. The body surface was smooth with no spines or bony tubercles. At 4 months after hatching, the fine spines present on the head and trunk of juveniles transformed into bony tubercles. At 7 months after hatching, fishes became sexually dimorphic including the position and development patterns of bony tubercles. Importantly, these sexually dimorphic changes in morphology corresponded closely with descriptions of different species. Specifically, females could be classified as Eumicrotremus asperrimus, and young and fully developed males as Cyclopteropsis bergi and Cyclopteropsis lindbergi, respectively. These observations resolved a previously ambiguous hypothesis regarding the taxonomy of these cyclopterid taxa. Cyclopteropsis bergi and C. lindbergi may be synonyms of E. asperrimus.