294 



Fishery Bulletin 90(2). 1992 



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Standard Length (mm) 



Figure 9 



Change in length of first caudal neural spine during development 

 of Dover sole Microstcnmis pacificus. Symbols represent Stage 1 (A), 

 Stage 2 (•), Stage 3 (■), Stage 4 (O), and Stage 5 (A). 



apparent loss. During the second year of life in 

 the plankton (see next section), body weight in- 

 creases an order of magnitude from a mean of 

 about 0.30g for Stage 1 in February to 2.0-4.0g 

 for Stage 2. All individuals that reach a size of 

 40mmSL are at least 0.74g; Stage-2 specimens 

 are at least 1.39g; Stage 3, at least 0.80g; and 

 Stage 4, at least l.Og. Because our sample size 

 for Stage 3 is relatively large, our best estimate 

 of a weight threshold for metamorphosis is 

 ~0.8g. However, if the suggestion of weight loss 

 during metamorphosis is not an artifact (Fig. 11), 

 the weight threshold may be closer to the mini- 

 mum weight of Stage 2. Further complicating an 

 estimate of that threshold is the observation that 

 our lightest Stage-2 specimen (42.6mm SL and 

 1.39g) was caught in January with a developmen- 

 tal score of 7, and presumably may already have 

 lost weight. 



Because SINT increases during metamorphosis 

 and BDIA decreases, the SINT/BDIA ratio pro- 

 vides an additional means of visualizing the rela- 

 tionship between the metamorphic process and 

 developmental stages (Fig. 12). 



Timing and duration of stages 



Temporal change in size of Stage-1 larvae <40mmSL 

 was analyzed using MPA (Fig. 13). Small larvae, about 

 6-8 mm, were foimd from February to June. The small- 

 est identifiable mode was in April, and from November 

 to March modes were level around 22-25 mm. Two 

 notable features of these data are apparent accelerated 

 growth in June and reduced availability of larger 



Figure 1 1 



Mean weight (horizontal line), weight interval for 50% of 

 observations (box), and weight range for Stages 2-4 in Dover 

 sole MicTostomvs pacificus. 



