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Fishery Bulletin 102(4) 



Figure 5 



Histological sections through ovaries of Rhabdosargus sarba showing 

 lAl the outer layers of a yolk granule oocyte, and postovulatory follicles in 

 the ovaries offish collected at (B) ca. 02:00, (C and D) ca. 18:30, (E) ca. 

 22:00 and ca. (F) 01:00 h. g=granulosa layer; lu = lumen; t = thecal layer; 

 yg=yolk granule; yv=yolk vesicle; zre = zona radiata externa. Scale bars = 

 25 ftm in A, and 50 pra in B-F. 



caught several R. sarba with new POFs in their ovaries 

 and hydrated oocytes in their oviducts, we were able to 

 catch only one individual of this species in which the 

 ovaries possessed new POFs and no hydrated oocytes. 

 The latter fish, which had clearly just completed spawn- 

 ing, was caught between 05:00 and 06:00 h. 



Several species are known typically to complete 

 spawning in the 10-14 hours after the time when their 

 oocytes commence hydration, e.g., the northern anchovy 

 (Engraulis mordax) (Hunter and Macewicz, 1985), the 

 spotted seatrout (Cynoscion nebulosus) (Brown-Peterson 

 et al., 1988) and the horse mackerel (Trachurus trachu- 

 rus) (Karlou-Riga and Economidis, 1997). Furthermore, 

 spawning is typically completed 2-5 hours after the 

 commencement of ovulation, e.g., the spotted seatrout 



(Cynoscion nebulosus) (Brown-Peterson et al., 1988), 

 the Black Sea anchovy [Engraulis encrasicholus) (Lisov- 

 enko and Andrianov, 1991) and the weakfish {Cynoscion 

 regalis) (Taylor and Villoso, 1994). These consistent 

 data, when considered in conjunction with the similar 

 duration of hydration of R. sarba, and the capture of a 

 very recently spawned fish between 05:00 and 06:00 h. 

 provide very strong circumstantial evidence that, in 

 the lower Swan River Estuary, R. sarba spawns mainly 

 between 02:00 and 06:00 h. 



The newest POFs in the ovaries of R. sarba caught 

 at dusk, i.e., at 18:30 h, had degenerated to an extent 

 similar to those of ca. 12-h-old POFs in the ovaries of 

 other species, e.g. the skipjack tuna (Katsuwonus pela- 

 mis) (Hunter et al., 1986) and the whitemouth croaker 



