NarimatSU et a\ : Reproductive biology of Dexistes rikuzenius 



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Oocyte diameter (urn) 



Figure 5 



Oocyte diameter distributions just before the spawning season of Rikuzen sole [Dexistes 

 rikuzenius). Oocyte diameter was divided into small-scale (less than 200 j<m) and 

 large-scale groups (more than 300 ,«m). 



Rikuzen sole require a long period of time 

 for vitellogenesis and therefore the repro- 

 ductive cycle may differ among areas. 



In some flatfishes, it has also been re- 

 ported that oocytes in the cortical alveoli 

 stage appear for only a short period of time 

 because they develop rapidly into the pri- 

 mary yolk stage (Yamamoto, 1956; Janssen 

 et al., 1995). In the present study, only a 

 small percentage of individuals contained 

 this stage of oocytes; however, cortical 

 alveoli were present throughout various 

 months from June to October and in Feb- 

 ruary. These results are similar to results 

 for other flatfish and may indicate that the 

 absence of cortical alveoli oocytes in some 

 ovaries does not represent an incontinuity 

 of oocyte composition. 



From October to December some females 

 possessed primary yolk-stage oocytes, 



