LAROCHE and RICHARDSON: REPRODUCTION OF NORTHERN ANCHOVY 



48° — 



46' 



44' 



42° — 



40' 



126" 



124° 



122° 



Figure l. — General region of the northeastern Pacific where 

 EngrauUs mordax from the northern subpopulation have been 

 collected. 



was calculated for preserved fish by dividing total 

 gonad w^eight by body weight (before gonad re- 

 moval) and multiplying the resultant value by 

 100. 



Oocytes from preserved ovaries were measured 

 to the nearest 0.02 mm at 50 x magnification with 

 an ocular micrometer in a dissecting microscope. 

 Oocyte diameter was measured until oocytes be- 

 came elliptical in shape, then length (longest di- 

 mension) was measured. Measurements were 

 made of approximately 200 oocytes/ maturing fish 

 (with oocytes S20.14 mm) and 100 oocytes/ 

 immature fish (with oocytes ^0.14 mm). Fish were 

 then grouped into 10 stages of ovarian develop- 

 ment, depending on the modal length of the 

 largest and most advanced group of oocytes in the 

 ovary (Clark 1934) (Table 2). The size intervals 

 used to define these ovarian stages were arbitrar- 

 ily chosen and do not necessarily represent actual 

 physiological stages of maturation. Composite 

 oocyte size-frequency distributions based on all 

 anchovies in each stage of ovarian development 

 were derived from the mean number of oocytes in 

 each 0.02 mm size class. 



Table 2. — Ten stages of ovarian development in Engraulis 

 mordax based on modal length of the most advemced oocytes and 

 the length interval containing the mode. 



Stage of Location of mode 



ovarian of advanced 



development oocytes (mm) 



Stage of 



ovarian 



development 



Location of mode 

 of advanced 

 oocytes (mm) 



Fecundity estimates were based on counts of 

 only the largest and most advanced oocytes ( vary- 

 ing with stage of ovarian development) in three, 

 wet weighed subsamples from the central region of 

 the left, preserved ovary. Chi-square tests of inde- 

 pendence indicated no significant difference 

 (P>0.05) in oocyte size-frequency distribution 

 among three different regions, anterior, central, 

 and posterior, within the left ovary or between the 

 central regions of either ovary. Each subsample, 

 consisting of a clump of oocytes, was lifted from the 

 ovary with a forceps and weighed to the nearest 0.1 

 mg. Subsample weights ranged from 10 to 50 mg. 

 Oocyte counts were made under a dissecting mi- 

 croscope after the subsample had been teased 

 apart in water. Each subsample yielded an esti- 

 mate of fecundity expressed as total number of 

 advanced oocytes contained in the ovaries, 

 number of advanced oocytes per gram total body 

 weight, and number of advanced ooctyes per gram 

 ovary-free body weight. The mean of these sub- 

 samples provided the fecundity estimate for each 



605 



