Temperature influence on 

 postovulatory follicle degeneration 

 in Atlantic menhaden, 

 Brevoortia tyrannus 



Gary R. Fitzhugh 



Department of Zoology, Box 7617 

 North Carolina State University 

 Raleigh, North Carolina 27695-761 7 



Present address: The institute for Fishery Resource Biology 



Florida State University 



and 



Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



3500 Delwood Beach Road, Panama City, Florida 32408-7403 



William F. Hettler 



Beaufort Laboratory, Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



101 Pivers Island Road, Beaufort, North Carolina 28516-9722 



The occurrence of postovulatory fol- 

 licles within the ovaries offish is a 

 positive indication of spawning, be- 

 cause they are the evacuated fol- 

 licles following ovulation. There- 

 fore, their frequency of occurrence 

 may be used to test factors influ- 

 encing reproduction. For example, 

 postovulatory follicles can be used 

 to estimate spawning frequency, 

 which in turn is used to estimate 

 spawning biomass (Hunter and 

 Macewicz, 1985). Their state of de- 

 generation can be assessed from 

 histological sections of the ovary to 

 estimate the time elapsed since 

 spawning for females sampled in 

 the wild. In addition, the occur- 

 rence of postovulatory follicles 

 might be useful to test hypotheses 

 about events that may trigger 

 spawning and benefit larval trans- 

 port (see Taylor, 1984; Checkley et 

 al., 1988). 



A requisite for applying this his- 

 tological method of determining 

 spawning frequency is validation of 

 the duration that postovulatory fol- 

 licles can be detected in field samples. 



This has been done through closely 

 timed observations of spawning in 

 the field and by laboratory-induced 

 spawning and subsequent sam- 

 pling of female gonads (Hunter and 

 Macewicz, 1985). Laboratory spawn- 

 ing offers more certainty in deter- 

 mining the time of spawning and 

 facilitates more precise measure- 

 ment of the degeneration time of 

 postovulatory follicles. Uncertainty 

 regarding the duration of post- 

 ovulatory follicles has led to ques- 

 tions about estimates of spawning 

 frequency (Brown-Peterson et al., 

 1988; Fitzhugh et al., 1993; and 

 Goldberg et al., 1984). Variation in 

 the duration of postovulatory follicles 

 may be largely due to the particular 

 species involved and its preferred 

 spawning temperature (Hunter and 

 Macewicz, 1985). 



Atlantic menhaden spawn across 

 a wide geographic range of U.S. 

 coastal Atlantic waters (Cape 

 Canaveral, Florida, to Martha's 

 Vineyard, Massachusetts) and 

 probably over a wide range of tem- 

 perature as well (Judy and Lewis, 



1983). Eggs have been collected 

 between the 15° and 20°C surface 

 isotherms in the mid-Atlantic Bight 

 (Kendall and Reintjes, 1974). We 

 wished to examine differences in 

 postovulatory follicle duration and 

 age at stage due to temperature in 

 Atlantic menhaden. As a prelimi- 

 nary step to future estimation of 

 spawning frequencies, our objective 

 was to characterize postovulatory 

 follicle degeneration and validate 

 postovulatory follicle duration for 

 Atlantic menhaden induced to 

 spawn at different temperatures in 

 the laboratory. 



Materials and methods 



Adult menhaden were collected 

 near Harker's Island, North Caro- 

 lina, between mid-August and mid- 

 September 1988, 1990, 1991, and 

 1992. During each period, menha- 

 den were maintained in outside 

 tanks under ambient flow-through 

 conditions until mid-October to 

 mid-November when they were 

 moved to inside tanks to begin 

 conditioning for spawning. We in- 

 duced spawning in either December 

 (1990) or March (1988, 1991, 1992) 

 with methods reported by Hettler 

 (1981). Menhaden of both sexes 

 were conditioned to spawn by 

 means of intraperitoneal injections 

 of human chorionic gonadotropin 

 (HCG) and carp pituitary extract 

 (CP). We gave injections between 

 0800 and 1000 hours on successive 

 days, and spawning usually oc- 

 curred the night following the sec- 

 ond (CP) injection. 



Spawning was induced under 

 three temperature regimes; 14.8- 

 15.7°C for one group in December 

 1990; 17.9-18.2°C for one group in 

 March 1992; and 19-20°C for 

 groups in March 1988, December 

 1990, and March 1991. Groups of 

 menhaden ranged from 22 to 31 



Manuscript accepted 13 March 1995. 

 Fishery Bulletin 93:568-572 ( 1995). 



568 



