McDermott et al: Annual fecundity, batch fecundity, and oocyte atresia of Pleurogrammus monopterygius 



23 



In order to deduct the population of 

 stage-4 oocytes from the whole population 

 of stage 5+ oocytes in prespawning-stage 

 ovaries, we determined the size overlap 

 between stage-4 and stage-5 oocytes by 

 examining histological sections from six 

 prespawning-stage ovaries. All oocytes 

 that had been sectioned through the nu- 

 cleus were measured with a compound 

 microscope and camera system with Op- 

 timas software. We determined that all 

 oocytes smaller than 525 um were stage-4 

 oocytes and did not overlap in size with 

 stage-5 oocytes in the prespawning-stage 

 ovaries (Fig. 3A). We used the postspawn- 

 ing-stage ovaries that had only stage-4 

 oocytes and atretic hydrated oocytes to 

 estimate the proportion of stage-4 oocytes 

 that was less then 525 f<m. This propor- 

 tion was then applied to the prespawn- 

 ing-stage ovaries to estimate the number 

 of stage-4 oocytes present. 



The total number of stage-4 oocytes in 

 the tissue sample for each prespawning- 

 stage ovary was estimated from 



and 





(1) 



(2) 



# 4" ^ # # 



B 



Ji 



1 



J 



1 



ifcl 



EIL. 



4" 



4? 4" ^ ^ 4? 



4" 4' 4 4" 4" 



Micrometers 



where h^, = estimated total number of 

 stage-4 oocytes in a tissue 

 sample of a prespawning 

 specimen /; 



c, = total number of stage-4 oocytes <525 f(m 

 in a tissue sample for a prespawning speci- 

 men i; 



p - the estimated proportion of total stage-4 

 oocytes <525 fim, estimated from ovaries 

 of a postspawning female; 



g, = total number of stage-4 oocytes <525 jum 



in postspawning-stage ovaries; and 

 m, = total number of all stage-4 oocytes in post- 

 spawning-stage ovaries. 



Estimation of potential annual fecundity and 

 batch) fecundity 



Potential annual fecundity and batch fecundity were cal- 

 culated by using prespawning specimens. Two scenarios 

 were examined for potential fecundity: 



Figure 3 



Combined size distributions of (A) stage 4 (clear bars) and stage 5 

 (black bars) oocytes from histological slides of six prespawning Atka 

 mackerel iPleurograrnmus monopterygius) specimens ( 1994); (B) stage-4 

 oocytes from prespawning (clear bars) and postspawning (black bars) 

 fish, measured from histological slides of 1993 and 1994 Atka mack- 

 erel specimen. 



n.O, 



W. 



(3) 



where f, = estimated potential fecundity or batch 

 fecundity for a prespawning specimen /; 

 n^ = number of oocytes in the tissue sample of a 

 prespawning specimen (for potential fecun- 

 dityjj,,^,: oocytes of stage 4 and greater; for 

 potential fecundity^j^g^g^ oocytes of stage 

 5+, for batch fecundity, number of hydrated 

 oocytes); 



= total ovary weight (g) for a prespawning 

 specimen ;; and 



= weight of tissue sample (g) for a prespawn- 

 ing specimen i. 



O. 



W. 



Scenario 1: potential fecundity, ^,^1 (counting oocytes 

 stage 4 and greater); and 



Scenario 2: potential fecundity^^j^ g^ (counting only 

 oocytes stage 5-i-). 



The following equation was used: 



Prespawning-stage ovaries that contained oocytes 

 in the early hydration stage (stage 7) or greater were 

 examined to estimate batch fecundity. Atka mackerel 

 appear to hydrate one batch of oocytes at a time and 

 the hydrated oocytes can be clearly separated from less 

 developed oocytes by a gap in oocyte-size distribution 

 (Fig. 2B). 



