NOTE Fargo and Tyler: Oocyte maturation in Pleuronectes vetulus 



195 



500 

 450 

 400 

 350 

 300 

 250 

 200 

 150 

 100 

 50 

 



500 

 450 



T 40 ° 

 I 350 \ 



4 300 



| 250 



-I 200 



§ 100 

 50 







30 



500 



450 



1" 400 



§ 350 



4 300 



I 250 



-1 200 



-£. 150 



<§ 100 



50 







30 



Aub-37 



° g ° 6 o o ° o; 



o provttolloflonlc 

 • vltsllogenic 

 — regression 



30 35 40 45 50 



Total length (cm) 



55 



Aug-88 



oggooe °86 oo 



35 



40 45 



Total length (cm) 



50 



55 



Aug-90 



• • 



OO OOq nOO 



35 



40 45 



Total length (cm) 



50 



55 



Figure 4 



Mean oocyte diameter vs fish length determined 

 from ovary samples collected from Hecate Strait 

 English sole {Pleuronectes vetulus) during the 

 month of August, 1987. 1988, and 1990. 



We also found no trend in the mean size of 

 previtellogenic oocytes among months within years, 

 contrary to results reported by Dunn and Tyler 

 (1969). One explanation for this is that the recruit- 

 ment of small immature (previtellogenic) oocytes 

 from the germinal epithelium is a continual process 

 for Hecate Strait English sole. Alternatively, there 

 may be a short time period, following spawning for 

 example, during which previtellogenic oocytes recruit 

 and quickly grow to a size of around 80 p. Additional 

 work is needed to resolve these possibilities. 



Spawning 



In general larger fish produced yolk earlier and 

 spawned earlier than smaller fish. Most of the 

 spawning fish were obtained from samples collected 

 in October and November but there was also evi- 

 dence of spring (March) spawning for smaller fish. 

 Egg size at the time of spawning did not appear to 

 be dependent on fish length. However, there is some 

 evidence from this study to suggest a possible mini- 

 mum size limit for eggs at the time of spawning. 

 That is, the difference in the mean diameter of 

 vitellogenic oocytes between smaller and larger fish 

 decreased over time until there was no apparent 

 difference at the time of spawning. Observations 

 made during this study indicate that atresia was not 

 as prevalent for Hecate Strait English sole as that 

 reported for English sole in Puget Sound by Johnson 

 et al. (1991). 



Marine fish species show wide variability in the 

 reproductive process, which enables them to miti- 

 gate the uncertain conditions in the marine environ- 

 ment (Murphy, 1968; Roff, 1981). English sole dem- 

 onstrate considerable phenotypic plasticity with 

 regard to spawning. In Hecate Strait the spawning 

 season extends from early fall through the follow- 



