Ganias et al : Degeneration of postovulartory follicles in Sordino pilchardus 



135 



ference in POF duration for the Iberian sardine across 

 the study years could never exceed 0.5 days, thus re- 

 ducing the concerns in relation to the potential bias 

 introduced by varying ambient temperatures in the 

 estimation of the spawning fraction. 



Discussion 



The incorrect attribution of age to POFs and the effect 

 of temperature on POF resorption rate constitute major 

 sources of potential bias in the determination of daily 

 spawning classes in routine applications of the DEPM 

 (Stratoudakis et al., 20061. Our method was devised as 

 an indirect way to test the above issues together with 

 the effect of laboratory processing, i.e., type of preserva- 

 tive and embedding material. The method is based on 

 the assumption that in species with 

 diel spawning synchronicity, such 

 as in S. pilchardus, daily classes of 

 spawning fish have, at any given 

 time, POFs of similar size. The first 

 task in our analysis was to refine 

 existing staging criteria for the 

 POFs of Sardina pilchardus. This 

 task was mainly attempted through 

 analyzing the frequency distribu- 

 tion of POF cross-sectional areas in 

 females caught simultaneously and 

 by inspecting POFs in each size-age 

 mode for differences in the cytomor- 

 phological characteristics. 



The main cytomorphological 

 changes during the degeneration 

 of POFs in sardine ovaries are 

 the gradual deterioration of the 

 structure of the follicular layers 

 and alterations in the dimensional 

 characteristics (shape and size), ac- 

 companied by a decrease in their 

 overall number in the slide. Histo- 



0.04 



0,03 



u. 0,02- 



O 



Q. 



01 - 



0,04 



0.02 



ff 0-00- 



^ -0,02- 



-0,04 



20 40 60 

 POF age (fi) 



14 15 16 17 18 

 Sea temperature (°C) 



Figure 5 



(A) Degeneration of the postovulatory follicle (POF) cross-sectional area 

 (POF area) with time elapsed from spawning (POF age) for the Iberian 

 sardine Sardina pilchardus; 0=resin ; • = paraffin. (B) Effect of ambient 

 temperature on the sardine POF cross-sectional area. 



