Hesp et al.: Timing and frequency of spawning and fecundity of Rhabdosargus sarba 



655 



Figure 4 



Histological sections of ovaries of individual Rhabdosargus sarba caught on 

 1 and 2September 2001 at ca. 18:30 h (A), 21:30 h (Cl and 00:30 h (E) and 

 photographs of the oocytes from the other lobe of the ovary of the same three 

 fish (B, D ,Fi. c = coalescing yolk and lipid; ho=hydrating oocyte; l = lipid 

 droplet; mn=migratory nucleus oocyte; n = nucleus; yg=yolk granule oocyte. 

 Scale bars = 200 fim in A, C, and D and 250 jim in B, D, and F. 



Discussion 



Oocyte hydration, ovulation, and spawning periods 



Because histological studies showed that the ovaries of 

 numerous fish caught on different occasions between 

 18:30 and 20:30 h did not contain recently formed POFs, 

 we deduced that these fish had not spawned in the 

 previous few hours. However, at this time, the ovaries 

 of many fish, that were designated macroscopically as 

 at stage V and stage VI, often contained numerous 

 migratory nucleus-stage oocytes and, towards the end 

 of this period, often a few oocytes in the early stages of 

 hydration. Although the frequency distributions of the 

 oocyte diameters offish examined on both 1 and 13 Sep- 



tember were still unimodal at 18:30 to 20:30 h, they had 

 become bimodal by 21:30 to 23:30 h (Fig. 3), reflecting 

 the fact that, by this time, numerous oocytes had become 

 markedly enlarged through hydration. The above data 

 demonstrate that hydration typically commences soon 

 after dusk. Furthermore, because a number of J?, sarba 

 caught between 01:30 and 04:30 h, and particularly 

 towards the end of this time interval, contained ovaries 

 undergoing ovulation and had newly formed POFs, the 

 period between the onset of hydration and commence- 

 ment of ovulation typically lasts about 7-10 hours, which 

 is very similar to the duration estimated for species 

 such as the black sea anchovy [Engraulis encrasicholus) 

 (Lisovenko and Andrianov, 1991) and ballyhoo (Hemir- 

 amphus brasiliensis) (McBride et al., 2003). Although we 



