Hunter et al : Fecundity, spawning, and maturity of Microstomus paaficus 



121 



200 400 600 aOO 1.000 1,200 1.400 1,600 



FEMALE WEIGHT (gm) 



Figure 9 



Batch fecundity of Dover sole Microstomus paaficus as a func- 

 tion of female weight (without ovary). Line is Yg = 10. IW for 

 the second through the penultimate spawning batches (filled 

 circles); triangles = first spawning batch; open circles = last 

 spawning batch. 



This computation indicated that the occurrence of 

 females with a atresia of advanced oocytes was 

 significantly affected by locality of the samples but not 

 by season. In short, more California females had one 

 or more a-atretic advanced oocytes in their ovary than 

 did Oregon females. 



Batch fecundity 



The first step in our analysis of batch fecundity (Yg) 

 was to determine if the batch size varied with the order 

 of spawning. Analysis of variance indicated that a 

 significant batch-order effect existed (Table 13). The 

 mean relative fecundity of the first (1) and last spawn- 

 ing batch (U) were significantly lower than the other 

 batches (Table 13). 



In eleven females, the only advanced oocytes left in 

 the ovary were two "hydrated" spawning batches 

 (Table 14). Each was in a different stage of develop- 

 ment: one was fully hydrated (last batch), and the 

 other was in the migratory nucleus stage (penultimate 

 batch). In all of the eleven females, the last batch was 

 always lower than the penultimate batch. The t-test 

 for paired differences confirmed the effect of batch 

 order on fecundity indicated by the ANOVA. The t-test 

 also had less potential for bias because we used absolute 

 rather than relative batch fecundity. The (-test in- 

 dicated that the fecundity of the last batch differed 

 from the penultimate batch {t 4.99, df 10, P 0.0005). 



We concluded that the batch size of a female Dover sole 

 did change over the spawning season, with the last and 

 the first batch being lower than the rest. 



We determined the relation between batch fecundity 

 and weight using regression analysis. We did not use 

 the first and last batches since they were lower than 

 the rest. The intercept for the regression of batch 

 fecundity on female weight did not differ from zero (a 

 2142; t 1.87, df 40, P 0.07). Therefore we forced the 

 regression line through 0, yielding the relationship 

 Yb = 10. IW, where female weight ranged from 148 to 

 1464 g (Fig. 9). This analysis indicated that the relative 

 batch fecundity of Dover sole is about 10 oocytes per 

 gram ovary-free female weight, except for the first and 

 last batch. The relative fecundity for the first and last 

 batches combined was also about 10 oocytes per gram 

 (1 and U in Table 13). Thus the number of potential 

 spawnings (S) per year can be calculated using S = 

 (Yfr/10)-i- 1, where Yp^ is the relative potential an- 

 nual fecundity (Yp/W; Yp from Eq. 10). This means 

 that the average 1kg female spawns its 83,000 ad- 

 vanced yolked oocytes in about nine batches. 



Sexual maturity 



To determine the optimal criteria for sexual maturity 

 in female Dover sole, we established six sets of histo- 

 logical criteria for maturity (Table 15). The first set of 

 criteria selects females with either advanced yolked 



