Metamorphosis and an overview of early-life-history stages in Dover sole Microstomus pacificus

Morphological changes during metamorphosis of Dover sole Microstomus pacificus are described from 2220 larvae and juveniles. Unlike most flounders, initiation of eye migration is uncoupled from metamorphosis and from the habitat change from planktonic to benthic. From initiation to completion, metamorphosis appears to take about 9 months, during which time there is little increase in body length. Available evidence indicates that most spawning off Oregon occurs in spring, with April and May as peak hatching months. Settlement from the plankton occurs in winter, with January to March as peak settlement months. Duration of planktonic life appears to be about 2 years, with a minimum duration of about 18 months. Metamorphosing larvae settle over a broad "landing" zone (55-377 m), quantitatively distinct from, but overlapping, the narrower spring nursery zone (40-170 m). As yet, there is no evidence of delayed metamorphosis. Metamorphosis is protracted, seems to be seasonally-triggered, and may involve a significant period during which larvae switch between midwater and bottom habitats.