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Fishery Bulletin 94(1). 1996 



and a secondary growth phase as in most teleosts 

 (Wallace and Selman, 1981; Mayer et al, 1988). The 

 secondary growth phase is characterized by yolk 

 deposition, nucleus migration to the animal pole, and 

 hydration. In particular, oocytes in early vitellogenic 

 stages (partially yolked), and advanced yolked oo- 

 cytes that were included in the mature horse mack- 

 erel females had the following characteristics: 



Partially yolked oocytes Yolk vesicle deposition 

 following by the appearance of yolk granules and the 

 formation of the zona radiata. 



Advanced oocytes Increase of yolk granules result- 

 ing in compact dense yolk spherules, which filled the 

 cytoplasm. The nucleus was eventually surrounded 

 by the lipid droplets. 



Reproductive cycle 



Atresia stages and atretic states During the whole 

 sampling period, 392 ovaries out of 1,152 females 

 sampled were sectioned, and 85 were identified as 

 immature, 143 as spawning, 87 as nonspawning, and 

 77 as postspawning (Table 1 ). Ninety-six ovaries were 

 found having a-atresia in advanced yolked oocytes 

 (Table 2). 



We observed atresia throughout the spawning pe- 

 riod in sequential stages — a(alpha), /3(beta), and S 

 (delta), (Fig. 2, A-C). The a- and 5-stages of atresia 

 showed similar characteristics to those described for 

 northern anchovy (Hunter and Macewicz, 1985b). 

 The y (gamma) stage atresia was not observed; this 

 may have been due to its short duration or to the 

 fact that the follicle passes directly from the p to the 

 S stage without passing through the intervening y 

 stage (Hunter and Macewicz, 1985, a and b). In ad- 

 dition, the low incidence of <5-stage atresia observed 

 in regressing ovaries of European horse mackerel in- 

 dicates that some follicles might be completely re- 



sorbed during the P stage. In particular, the /3-stage 

 atretic follicle of European horse mackerel was char- 

 acterized by the presence of many vacuoles, possible 

 remnants of the lipid droplets that take longer than 

 yolk to be absorbed (Macewicz and Hunter, 1993). 



The spawning potential of females with atretic 

 ovaries is generally thought to be low (Hunter and 

 Macewicz, 1985b). To verify this expectation in the 

 regressing ovaries of European horse mackerel, we 

 estimated the percentages of females with the histo- 

 logical criteria of imminent spawning, past spawn- 

 ing, and nonspawning, which were classified into 

 atretic states 1 and 2. Females in atretic state 1 

 showed evidence of past or imminent spawning 

 (82.9% ), whereas the percentage of spawning females 

 in atretic state 2 was very low (7.7%) (Table 2). By 

 the time that ovaries reached atretic state 2, more 

 than half of the advanced yolked oocytes were not 

 viable. In particular, about 80% of the ovaries in 

 atretic state 2 had 90-100% atretic advanced yolked 

 oocytes. 



During this study, we identified two successive 

 reproductive seasons, the first one from October 1989 

 to early July 1990, and the second one from Decem- 

 ber 1990 to May 1991. Onset of spawning was ob- 

 served in December and January, respectively, and 

 continued until July and May of the first and second 

 seasons, respectively. In June 1990, no ovaries were 

 sectioned because females were macroscopically clas- 

 sified as immature, whereas in July 1990 all but one 

 (spawning) of the females were late postspawning 

 (atretic state 3). 



On the basis of histological classification of ova- 

 ries, 192 and 115 mature females were examined in 

 the first and second reproductive seasons, respec- 

 tively. The occurrence of a atresia was seen from the 

 onset of spawning. During the first spawning season 

 we observed that atretic state 1 was the most com- 

 mon atretic condition (Fig. 3A). Females in atretic 



