FISHERY BULLETIN. VOL. 78, NO. 3 



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that were arranged in increasing order of matur- 

 ity (Figure 4). Only fish taken in March and May 

 before the spawning season were used for the 

 curves of stages 1-8, although fish in these stages 

 were taken in other months. Stage 10 fish, charac- 

 terized by the presence of hydrated oocytes, were 

 taken only in July. Few oocytes in the 0.90-0.98 

 mm size range were seen and no stage 9 fish were 

 found. This apparent break in size distribution 

 was caused by rapid hydration of oocytes during 

 final maturation to ripe oocytes >0.90 mm. The 

 increase in oocyte size during hydration is illus- 

 trated by the comparison of oocyte size distribu- 

 tions in stage 10 fish before and after ovulation 

 (the release of oocytes from their follicles just prior 

 to spawning) (Figure 5). 



The most mature group of oocytes first began to 

 form a distinct mode in stage 4 ovaries. Secondary 

 modes of early yolked oocytes also appeared in 

 stage 4 and were present in stages 5 through 10 but 

 one of these groups never separated from the yolk- 

 less oocytes to form a distinct intermediate mode. 

 These same groups of early yolked oocytes, espe- 

 cially the mode between 0.45 and 0.50 mm, were in 

 essentially the same position in the oocyte size 

 distributions of spent and ovulated stage 10 fish 

 (Figure 5). 



At least two stages of oocyte maturation prior to 

 hydration were indicated by two modes in the 

 size-frequency distributions of all completely 

 opaque oocytes in weighed subsamples from two 



1 o^o ooooooooooo 

 o^o'C o' d d o d d —  — —  — ' 

 OOCYTE LENGTH (mm) 



o o 



OOCYTE LENGTH (mm) 



Figure 4. — Composite oocyte size-frequency curves represent- 

 ing nine stages of ovarian development in Engraulis mordax. (N 

 = no. offish.) 



Figure 5. — Composite oocyte size-frequency curves from north- 

 em anchovies in ovarian stage 10, before and after ovulation, and 

 in spent condition. (A^ = no. offish.) 



610 



