NOTE Fargo and Tyler: Oocyte maturation in Pleuronectes vetulus 



193 



33 cm 



prevHellogenlc 



60 110 160 210 260 310 360 410 460 

 Oocyte diameter (microns) 



42 cm 



prevHellogenlc 



60 110 160 210 260 310 360 410 460 

 Oocyte diameter (microns) 



38 cm 



10 60 110 160 210 260 310 360 410 460 

 Oocyte diameter (microns) 



46 cm 



| vltellogenlc 

 prevHellogenlc 



10 60 110 160 210 260 310 360 410 460 

 Oocyte diameter (microns) 



Figure 2 



Oocyte size compositions determined from ovary samples collected from Hecate Strait English sole 

 {Pleuronectes vetulus) in August 1988. 



the two years (Table 3). However, there were signifi- 

 cant differences in mean diameter for previtellogenic 

 oocytes among months within both years (Table 4). 

 No obvious trend in mean diameter over time was 

 apparent for previtellogenic oocytes. There were sig- 

 nificant differences in the rate of oocyte development 

 between 1987 and 1988 (Table 3). The mean diam- 

 eter of vitellogenic oocytes in June and August of 

 1987 was significantly larger than for the same 

 months in 1988, suggesting that vitellogenesis oc- 

 curred earlier in 1987 than in 1988. There were also 

 significant differences in the mean diameter of 

 vitellogenic oocytes among months within years 

 (Table 5). The mean diameter of vitellogenic oocytes 

 increased significantly, coinciding with advancing 

 oocyte development, between June-November in 

 1987 and June-October in 1988. 



Spawning 



Ovaries obtained from spawning fish (October 1988, 

 1990 and November 1987, 1990) were examined to 

 investigate 1) size-dependent spawning and 2) the 



relation between fish length and egg diameter at the 

 time of spawning. For the October 1988 sample, we 

 observed the presence of vitellogenic oocytes only in 

 fish smaller than 40 cm. The mean diameter of 

 vitellogenic oocytes in these fish ranged from 287 to 

 408 p. Fish ranging in length from 43 to 52 cm con- 

 tained spent ovaries with previtellogenic oocytes 

 only. Thus, we concluded that the larger fish had 

 spawned prior to the time of the sample collection. 

 In the October 1990 sample, taken two weeks ear- 

 lier than the 1988 sample, some of the fish larger 

 than 40 cm contained hydrated oocytes while oth- 

 ers had spent ovaries with resorbing oocytes, sug- 

 gesting that they were spawning in early October. 

 Oocytes examined from samples collected in Novem- 

 ber (1987, 1990) also indicated that larger fish had 

 spawned previous to this time. Fish larger than 42 

 cm contained only pre-vitellogenic oocytes and there 

 was no sign of resorbing oocytes. Most smaller fish 

 were in spawning condition during this month. 

 Vitellogenic oocytes were present in fish ranging 

 from 30 to 42 cm. Mean diameter ranged from 373 

 to 483 p and these oocytes were hydrated and trans- 



