NOTE Fitzhugh and Hettler. Postovulatory follicle degeneration in Brevoortia tyrannus 



571 



All spawning was estimated to have occurred be- 

 tween 2100 and 0200 hours and time from spawning 

 was recorded at each sampling period. We compared 

 histological states associated with these sampling 

 periods by standardizing the time of spawning (mid- 

 night, hour-0; Fig. 2). In general, events associated 

 with induction of spawning slowed down in the cold 

 temperature regime. Spawning at 14.8-15.7°C oc- 

 curred about 63 hours after HCG injection and about 

 39 hours after CP injection. However, within the 

 warmest series, spawning occurred about 34 and 11 

 hours, respectively, after HCG and CP injections. 



We saw characteristics of initial follicle degenera- 

 tion about 6 to 12 hours after spawning for all three 

 temperature regimes (Fig. 2, Table 1). There was an 

 apparent difference in overall duration of post- 

 ovulatory follicles between the high and low tempera- 

 ture regimes. Filling of the lumen (stage 3) was evi- 

 dent at the warm regime by about 21 to 46 hours 

 (Fig. 2). At 19-20°C, postovulatory follicles were dif- 

 ficult to distinguish (stage 4) as early as 36 hours, 

 but at the two colder regimes, postovulatory follicle 

 degeneration was not as advanced even at 58 hours 

 (e.g. stage 3, Fig. 2). Postovulatory follicle duration at 

 15°C is probably longer than 60 hours after spawning. 



Transition to successive atretic stages was appar- 

 ently faster at the warmest temperature and there 

 was some overlap of atretic stages at a given time 

 following spawning. For example, stages 1, 2, and 3 

 were observed at 20 hours from females held at 19- 

 20°C (Fig. 2). This overlap may be due to variation 

 in degeneration rates among females, the subjectiv- 

 ity of stage classification across a continuum of fol- 

 licle degeneration, or to variation in the exact time 

 of ovulation among females (because time from 

 spawning was estimated for all the females in a group 

 from a sample of fertilized eggs). A more precise 

 analysis of the durations for the various stages of 

 atresia would have been facilitated by sampling each 

 group at constant intervals after the spawning of eggs 

 and by using a larger sample size — particularly for 

 the coldest treatment. 



Observations of postovulatory follicle duration vary 

 for species that spawn at different temperatures. We 

 observed durations ranging from about 36 to over 60 

 hours for Atlantic menhaden spawning from 15 to 

 20°C. At similar temperatures (13 to 19°C), north- 

 ern anchovy, Engraulis mordax, Peruvian anchovy, 

 Engraulis ringens, and Pacific sardine, Sardinops 

 sagax, have postovulatory follicles that last about 48 

 hours (Hunter and Macewicz, 1985). Skipjack tuna, 

 Katsuwonus pelamis, and Hawaiian anchovy, 

 Encrasicholina purpurea, spawn at approximately 

 25°C and have postovulatory follicles that last about 

 24 hours (Hunter et al., 1986; Clarke, 1987). The 



dragonet Callionymus enneactis spawns at 28— 30°C 

 and has a postovulatory follicle duration less than 

 15 hours (Takita et al., 1983). Collectively, these ob- 

 servations confirm that increasing temperatures 

 decrease the time that postovulatory follicles can be 

 detected in fishes. 



The ability to identify the stage of postovulatory 

 follicles in order to determine spawning frequencies 

 becomes more important as their duration increases. 

 If postovulatory follicles are known to last less than 

 24 hours, females possessing them can be defined 

 with certainty as having day-0 postspawning ova- 

 ries for purposes of estimating spawning frequency. 

 Hunter and Goldberg (1980) and Hunter and 

 Macewicz (1985) developed this approach on the ba- 

 sis of the appearance of various features and assigned 

 day-0 and day-1 classifications to fish known to have 

 postovulatory follicle durations of about 48 hours. 

 However, if durations are known to be longer, knowl- 

 edge of the age of particular features of postovulatory 

 follicles becomes more critical in classifying 

 postspawning ovaries. We focused on the alignment 

 of the granulosa layer (and nuclei), on the presence 

 of vacuoles, and the appearance of the lumen for iden- 

 tifying stages because these features were easily rec- 

 ognizable in Atlantic menhaden postovulatory fol- 

 licles and could be used to classify fairly discrete 



