POSTOVULATORY FOLLICLE HISTOLOGY OF 



THE PACIFIC SARDINE, SARDINOPS SAGAX, 



FROM PERU' 



The use of the postovulatory follicle as a means of 

 estimating incidence of spawning in multiple 

 spawning fishes was originally developed by 

 Hunter and Goldberg (1980) for the northern an- 

 chovy, Engraulis mordax, from southern Califor- 

 nia. This technique has proven to be quite useful 

 for biomass assessment using the "Egg Production 

 Method" (Parker 1980). 



As a result of this work, the postovulatory folli- 

 cle has assumed new importance. In the work of 

 Hunter and Goldberg (1980), E. mordax were 

 spawned artificially in the laboratory (Leong 

 1971). Fish were sacrificed at different time inter- 

 vals, and histological conditions of the postovula- 

 tory follicles were noted. As an alternative to this 

 method, in the current report we have aged post- 

 ovulatory follicles of the Pacific sardine, Sar- 

 dinops sagax, from Peru by establishing the time 

 of spawning (egg collections) and by making 

 periodic collections of S. sagax. 



Methods 



Samples of Sardi?2ops sagax were collected dur- 

 ing September-October 1982 near Chimbote, Peru 

 (lat 09°05', long. 78°35' ). Ovaries were preserved 

 immediately on collection in 10** neutral, buffered 

 Formalin 2 . Later, samples from a total of 270 

 ovaries were dehydrated in ethyl alcohol and em- 

 bedded in Paraplast. Histological sections were 

 cut at 6/x. Slides were stained with Heidenhain's 

 iron hematoxylin or Harris' hematoxylin followed 

 by eosin counterstain. 



Sardine egg samples from Peru indicated 0100 h 

 to be the midpoint of the daily spawning interval 

 ( Smith 3 ). Therefore, by knowing the hour of collec- 

 tion and assuming that spawning occurred around 

 0100 h, we calculated the approximate age of post- 

 ovulatory follicles. 



Results and Discussion 



The sardine is a multiple spawning fish (Clark 

 1934), and during the spawning season we typi- 



■Publication No. 11 of PROCOPA. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



3 P.E. Smith, Southwest Fisheries Center La Jolla Laboratory, 

 National Marine Fisheries Service, NOAA, P.O. Box 271, La 

 Jolla, CA 92038, pers. commun. March 1983. 



cally observe a mature yolk-filled mode of eggs 

 representing the next spawning session and a vi- 

 tellogenic mode for a subsequent spawning. 



Postovulatory follicle. Day 

 (0-6 h after spawning) 



The new S. sagax postovulatory follicles (Fig. 

 1A, B) were striking in their strong resemblance to 

 the age 0-day postovulatory follicles of E. mordax 

 (elapsed time from spawning <24 h) (Hunter and 

 Goldberg 1980). The newly formed follicles of S. 

 sagax contained many involutions or corrugations 

 and were composed of columnar epithelium rest- 

 ing on a connective tissue theca. Nuclei had a 

 basal location. The lumina occasionally contained 

 eosinophilic granules of unknown origin (Hunter 

 and Goldberg 1980) similar to those reported in 

 the newly formed postovulatory follicles of E. 

 mordax. 



Postovulatory follicle, Day 1 

 (7-30 h after spawning) 



These structures showed the beginning ( Fig. 1C ) 

 of a breakdown in organization in comparison to 

 day-0 postovulatory follicles. This included a size 

 decrease to about one-half and marked degenera- 

 tion of the columnar epithelial cell lining. Many 

 epithelial cells had irregular shapes, vacuoles, 

 and pycnotic nuclei. The convoluted structure was 

 not as distinct as in day-0 postovulatory follicles. 

 The linear arrangement of columnar epithelial 

 cells was still evident. This is important, and con- 

 stitutes the chief character that should be used for 

 distinguishing day-1 from day-2 postovulatory fol- 

 licles in S. sagax. This linear arrangement was 

 absent in day-2 S. sagax postovulatory follicles. 



Postovulatory follicle, Day 2 

 (31-53 h after spawning) 



Degeneration of the S. sagax postovulatory fol- 

 licle was clearly more advanced (Fig. ID) at this 

 stage. Distinguishing them from old atretic folli- 

 cles is now a critical problem. Lumina were typi- 

 cally occluded and contained irregularly shaped 

 cells with pycnotic nuclei, representing the final 

 stages in the degeneration of the columnar epithe- 

 lial cells that were previously so evident (Figs. 1A, 

 B) in day-0 S. sagax postovulatory follicles. Vac- 

 uoles may be present. While the greatly convo- 

 luted structure that characterized earlier post- 

 ovulatory follicles is no longer pronounced, there 



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