NOTE Fargo and Tyler: Oocyte maturation in Pleuronectes vetulus 



191 



graphs of the stages of matura- 

 tion for English sole oocytes 

 have been summarized by 

 Fargo and Sexton (1991). 4 Ex- 

 amples of oocyte size distribu- 

 tions for fish of different 

 lengths sampled during the 

 same period, August 1988, are 

 presented in Figure 2. For all 

 sizes of English sole collected, 

 we observed the simultaneous 

 presence of only two modes in 

 the oocyte size distributions. 

 The smaller mode (10-150 u> 

 consisted of previtellogenic oo- 

 cytes and the larger mode 

 (150-500 u) of vitellogenic oo- 

 cytes. No previtellogenic oo- 

 ctyes >150 u were observed. 

 The size modes for previtel- 

 logenic oocytes were similar 

 among fish ranging in size from 

 33 to 46 cm. The mode for 

 vitellogenic oocytes shifted to 

 the right (increased) with in- 

 creasing fish length. 



Vitellogenic oocytes in- 

 creased in size from early sum- 

 mer until they became hy- 

 drated prior to spawning in the 

 fall (Fig. 3). We observed no 

 trend in the size composition of 

 previtellogenic oocytes over the 

 same period. As the month of 

 spawning was approached a 

 complete separation between 

 the two modes became appar- 

 ent. The irregular shape of the 

 modal distribution for vitel- 

 logenic oocytes in Figure 3 is 

 caused by combining data for 

 fish of different lengths and de- 

 veloping at different rates. The 

 more normal distribution for 

 this mode during the month of 

 spawning is due to two factors. 

 First, the size range of fish for 

 this sample was smaller than 

 for other samples and, second, 

 egg diameter at the time of 

 spawning was similar for fish 

 of different length. Fargo and 

 Sexton (1991) 4 described the 

 events of oocyte maturation for 

 English sole in detail. Briefly, 



