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Fishery Bulletin 105(1) 



Figure 6 



Microphotographs of very early-stage postovulatory follicles from the female Iberian sardine 

 Sardina pilchardus, captured during the daily spawning period. Embedding materials used in 

 the experiment were (A) resin; (B) paraffin. 



logical changes in the granulosa seem to follow the 

 general pattern of degeneration described for other 

 populations of sardine (Japanese sardine [Sardinops 

 melanostictus]: Murayama et al., 1994; Mediterranean 

 sardine [S. pilchardus]: Ganias et al., 2003; Pacific 

 sardine [Sardinops sagax]: Goldberg et al., 1984; South 

 African sardine [S. sagax]: Akkers et al., 1996) and oth- 

 er fish species (see interspecific comparison in Hunter 

 and Macewicz, 1985). The information provided in our 

 study mostly concerns the changes in the dimensional 

 characteristics of POFs and how these may be used in 

 the aging of these POFs. 



The evolution in the shape of POFs is allometric be- 

 cause the POF surface along the lamellar epithelium 

 decreases at a lower rate than the overall area of the 

 follicles. As a result, throughout degeneration, POFs 

 passed consecutively from an irregular to a semirectan- 

 gular and finally a triangular shape, providing a useful 

 additional morphological criterion for determining the 

 stage of the POF. POFs remain for the whole of their 

 "life" on the epithelium of the lamellae, where they oc- 

 cupy approximately the space of an oocyte at the yolk 

 vesicle stage (early POFs) or of a primary oocyte (late 

 POFs). For an indeterminate spawner like sardine, 

 where recruitment of new spawning batches of oocytes 

 occurs continuously and directly from the oogonia, fast 

 resorption is necessary because the aggregation of old 

 POFs would restrict the space available for the devel- 

 opment of new oocytes. On the other hand, late atretic 

 pre-ovulatory follicles separate from the epithelium 

 and concentrate medially in the lamellae — a pattern 

 that has also been observed in other fish species such 

 as striped mullet (Mugil cephalus) (McDonough et al., 

 2005). Late atretic follicles remain in fish ovaries for 



long periods, which might extend up to the next spawn- 

 ing season (Hunter and Lo, 1997; Miranda et al., 1999). 

 Therefore, their separation from the lamellar epithelium 

 possibly constitutes a mechanism for managing space 

 availability for the newly recruited spawning batches. 

 The aforementioned morphological phases and the 

 different histological characteristics of the granulosa 

 layer were used, together with follicle size, in the aging 

 of POFs. Four daily classes were identified, implying 

 that full POF resorption in the Iberian sardine ex- 

 ceeded 72 hours. The duration of POF degeneration is 

 variable among fish species, ranging from less than 1 

 day in the skipjack tuna {Katsuwonus pelainis) (Hunter 

 et al., 1986) to more than 7 days in the piau-jejo (L. 

 taeniatus) (Santos et al., 2005). However, there are 

 reports of intraspecific variability in the duration of 

 POF resorption, both under laboratory conditions (e.g., 

 Atlantic menhaden, Brevoortia tyrannus; Fitzhugh and 

 Hettler, 1995) and in the field (e.g., spotted seatrout 

 [Cynoscion nebulosus]: Roumillat and Brouwer, 2004). 

 In some cases the duration of POF resorption is under- 

 estimated because late POFs can be confused with late 

 atretic stages (e.g., northern anchovy [Engraulis mor- 

 dax] Hunter and Macewicz, 1980). However, given that 

 surveys for refining the DEPM are undertaken at peak 

 spawning months (Stratoudakis et al., 2006), POFs 

 would so greatly outnumber atretic follicles in fish ova- 

 ries that there would be little confusion in distinguish- 

 ing the two and thus would lead to a very minor bias in 

 the duration of POF resorption. In addition, POFs in S. 

 pilchardus are effectively distinguished from all types 

 of atresia, and this distinction has been confirmed by 

 the high degree of consistency in the scoring of post- 

 ovulatory and atretic follicles by different observers. At 



