Baelde Biology and dynamics of reproduction in Hyperoglyphe antarctica 



209 



Females 



Nonspawning period 



Males 



4? SO 55 60 65 70 75 SO 85 90 95 100 



50 55 60 65 70 75 80 85 90 



Spawning period 



45 50 55 60 65 70 75 80 85 90 ms [00 



50 55 60 65 70 75 80 85 90 



Fork length (em) 

 Figure 10 



Comparison by sex of frequency distributions between "nonspawning" I May to December) and 

 "spawning" (January to April) periods (years combined) for blue-eye trevalla, Hyperoglyphe 

 antarctica. For females, most common maturity status is indicated for different size groups (see 

 text), n - sample size. 



that there had been no changes in the size at matu- 

 rity of blue-eye trevalla since the fishery began. 



The fecundity of blue-eye trevalla is clearly deter- 

 minate; several batches of ripe oocytes are formed 

 successively from a standing stock of yolked oocytes. 

 Comparison of annual and batch fecundities suggests 

 that females spawn all their oocytes in 3 or 4 large 

 batches. Several studies (e.g. Macewicz and Hunter, 

 1993; Oda et al., 1993 ) have shown that postovulatory 

 follicles usually persist in fish ovaries for short peri- 

 ods (days). The cooccurrence of postovulatory follicles 

 and ripe oocytes in ovaries of blue-eye trevalla also 

 suggests that hydration and ovulation of successive 

 batches could take place within a short period. How- 

 ever, multiple samples taken at short intervals dur- 

 ing spawning would be required to age postovulatory 

 follicles accurately. 



The average relative fecundity of blue-eye trevalla 

 appears to be fairly high when compared with other 



middle slope species (e.g. hoki, Macruronus novaezel- 

 andiae off southern Australia [520 oocytes/g 5 ] and 

 sablefish, Anoplopoma fimbria off Oregon [110 oo- 

 cytes/g [Macewicz and Hunter, 1994]). The rate of 

 atresia in ovaries appears to be negligible, and, in 

 the present study, it did not affect fecundity estimates 

 (although this would not necessarily be true for all 

 spawning seasons). The fact that female blue-eye 

 trevalla are partial spawners constitutes more of a 

 problem for estimating fecundity, even more so be- 

 cause spawning batches are large. Partially spent 

 females cannot be identified macroscopically, and to 

 avoid underestimating annual fecundity, it is neces- 

 sary to check microscopically for the presence of post- 

 ovulatory follicles in every female before estimating 

 the number of oocytes. 



5 Bulman, C. CSIRO, Division of Fisheries, Hobart, Tas- 

 mania. Personal commun. 



