Abstract.- Morphological changes 

 during metamorphosis of Dover sole 

 Microstomics padficus are described 

 from 2220 larvae and juveniles. Un- 

 like most flounders, initiation of eye 

 migration is uncoupled from meta- 

 morphosis and from the habitat 

 change from planktonic to benthic. 

 Dover sole larvae are optically asjrm- 

 metrical during most of their plank- 

 tonic life. Major features associated 

 with metamorphosis are reduction 

 in body depth with associated reduc- 

 tions in lengths of neural and hemal 

 spines, increase in relative eye diam- 

 eter, loss of canine-like teeth coin- 

 cidental with acquisition of incisor- 

 like teeth, resorption of posterior 

 process of coracoid, development of 

 body scales, change in body pigmen- 

 tation, and development of the gut 

 loop in the secondary body cavity. 

 From initiation to completion, meta- 

 morphosis 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 (40-170m). As 

 yet, there is no evidence of delayed 

 metamorphosis. Metamorphosis is 

 protracted, seems to be seasonally- 

 triggered, and may involve a signif- 

 icant period during which larvae 

 switch between midwater and bot- 

 tom habitats. 



Metamorphosis and an overview 

 of early-life-hiistory stages in Dover 

 sole Microstomus padficus* 



Douglas F. Markle 

 Phillip IVI. Harris 

 Christopher L. Toole 



Department of Fisheries and Wildlife, 104 Nash Hall 

 Oregon State University, Corvallis, Oregon 97331-3803 



There is uncertainty about the length 

 of the pelagic life of Dover sole Micro- 

 stomus pacificus. Hagerman (1952) 

 noted that the "pelagic life is pro- 

 longed for several months and meta- 

 morphosis is delayed." Allen and 

 Mearns (1977) thought a 9-month 

 planktonic stage was "probably 

 not unusual." Pearcy et al. (1977a) 

 examined the early life history in 

 greater detail and concluded that 

 "Dover sole larvae are pelagic for at 

 least a year." Hayman and Tyler 

 (1980), although citing Pearcy et al. 

 (1977a), constructed a time-line in- 

 dicating a 9-month pelagic larval 

 stage. 



There is also little agreement on 

 estimated body length at the end of 

 the first year of life. Pearcy et al. 

 (1977a) estimated growth to be 20-30 

 mm standard length (SL) during the 

 first year, but also concluded that 

 metamorphosis took place after 

 about 1 year at 30-50 mm SL (the 

 extra 10-30 mm of growth was not 

 explained). Hagerman (1952) and 

 Demory (1972), both limited by small 

 sample sizes, mention lengths of 66- 

 75 mm total length (TL) for nominal 

 1-year-old specimens. 



Uncertainty about duration and 

 growth in the pelagic phase has im- 

 portant implications for age esti- 

 mates. Whether based on scales or 

 otolith sections, no researcher has 



Manuscript accepted 18 March 1992. 

 Fishery Bulletin, U.S. 90:285-301 (1992). 



'Technical paper 9837, Oregon State Univer- 

 sity Agricultural Experiment Station. 



documented the age or size at which 

 the first nominal annulus forms 

 (Demory 1972, Chilton and Beamish 

 1982, Pikitch and Demory 1988, 

 Hunter et al. 1990). 



From the large midwater trawl col- 

 lections made by W.G. Pearcy and 

 colleagues (OSU) from 1961 to 1982, 

 and juvenile bottom-trawl surveys 

 conducted off Oregon from 1988 to 

 1990, we describe metamorphosis 

 and other stages in the early life 

 history of Dover sole and address 

 questions relating to the duration and 

 timing of these stages. 



Materials and methods 



Midwater trawl collections 



A total of 796 Dover sole larvae were 

 obtained from 425 midwater trawl 

 stations off Oregon. Details of sam- 

 pling methods are given in Pearcy 

 (1976, 1980) and Pearcy et al. (1977 

 a,b). Because the midwater trawls 

 were made for a variety of reasons, 

 there are constraints on interpreta- 

 tion of these data. The most impor- 

 tant constraints are seasonal, diel, 

 depth, and gear. Seasonal coverage 

 was best from June to September, 

 and poorest in May and October 

 (Table 1). There was a pronounced 

 diel bias. Relatively few samples 

 were collected between 0600 and 

 2000 hours (Table 2). Most samples 

 were collected at night between 2200 

 and 0500 hours. The range of collec- 



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