648 



Abstract — We have studied the repro- 

 ductive biology of the goldlined sea- 

 bream (Rhabdosargus sarba) in the 

 lower Swan River Estuary in Western 

 Australia, focusing particularly on 

 elucidating the factors influencing 

 the duration, timing, and frequency 

 of spawning and on determining 

 potential annual fecundity. Our 

 results demonstrate that 1) Rhab- 

 dosargus sarba has indeterminate 

 fecundity, 2) oocyte hydration com- 

 mences soon after dusk (ca. 18:30 hi 

 and is complete by ca. 01:30-04:30 h 

 and 3) fish with ovaries containing 

 migratory nucleus oocytes, hyd rated 

 oocytes, or postovulatory follicles were 

 caught between July and November. 

 However, in July and August, their 

 prevalence was low, whereas that of 

 fish with ovaries containing substan- 

 tial numbers of atretic yolk granule 

 oocytes was high. Thus, spawning 

 activity did not start to peak until 

 September (early spring), when salini- 

 ties were rising markedly from their 

 winter minima. The prevalence of 

 spawning was positively correlated 

 with tidal height and was greatest 

 on days when the tide changed from 

 flood to ebb at ca. 06:00 h. i.e., just 

 after spawning had ceased. Because 

 our estimate of the average daily 

 prevalence of spawning by females 

 during the spawning season (July 

 to November) was 36.5%, individual 

 females were estimated to spawn, 

 on average, at intervals of about 2.7 

 days and thus about 45 times during 

 that period. Therefore, because female 

 R. sarba with total lengths of 180, 

 220, and 260 mm were estimated to 

 have batch fecundities of about 4500, 

 7700, and 12,400 eggs, respectively, 

 they had potential annual fecundities 

 of about 204,300, 346,100 and 557,500 

 eggs, respectively. Because spawn- 

 ing occurs just prior to strong ebb 

 tides, the eggs of/?, sarba are likely 

 to be transported out of the estuary 

 into coastal waters where salini- 

 ties remain at ca. 359«. Such down- 

 stream transport would account for 

 the fact that, although R. sarba exhib- 

 its substantial spawning activity in 

 the lower Swan River Estuary, few 

 of its early juveniles are recruited 

 into the nearshore shallow waters of 

 this estuary. 



Manuscript submitted 9 June 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 28 April 2004 by the Scientific Editor. 



Fish. Bull. 102:648-660(2004). 



Factors influencing the timing and frequency of 

 spawning and fecundity of the goldlined seabream 

 (Rhabdosargus sarba) (Sparidae) 

 in the lower reaches of an estuary 



S. Alexander Hesp 



Ian C. Potter 



Centre for Fish and Fisheries Research 



School of Biological Sciences and Biotechnology 



Murdoch University 



South Street 



Murdoch, Western Australia 6150, Australia 



E-mail address (for I C Potter, contact author): i.pottera'murdoch edu.au 



Sonja R. M. Schubert 



Ernst-Moritz Arndt Universitaet, Hansestadt Greifswald 

 F.-L.-Jahn StraBe 15a 

 17487 Greifswald, Germany 



The goldlined seabream {Rhabdosar- 

 gus sarba) is an important recreational 

 and commercial fish species in numer- 

 ous regions throughout the Indo-west 

 Pacific (van der Elst, 1988; El-Agamy, 

 1989; Kuiter, 1993). Although this 

 species is a protandrous hermaphro- 

 dite in certain regions, e.g., the waters 

 of Hong Kong and South Africa (Yeung 

 and Chan, 1987; Garratt, 1993). it is a 

 rudimentary hermaphrodite in a range 

 of environments in Western Australia 

 (Hesp and Potter, 2003). Rudimentary 

 hermaphrodites are those species in 

 which the juveniles possess gonads 

 consisting of both immature testicular 

 and ovarian tissues that, in adults, 

 develop permanently into either func- 

 tional testes with rudimentary ovar- 

 ian tissue or functional ovaries with 

 rudimentary testicular tissue (Buxton 

 and Garratt, 1990). In Western Aus- 

 tralia, R. sarba attains similar maxi- 

 mum lengths, i.e., 346-370 mm, in 

 temperate marine coastal waters and 

 the lower reaches of the Swan River 

 Estuary on the lower west coast of 

 Australia and in a large subtropical 

 embayment ca. 800 km farther north 

 (Hesp et al., 2004). However, the max- 

 imum age recorded for this species in 

 the estuary. 7 years, was far less than 

 that for the other two environments: 

 temperate marine coastal waters (11 



years) and a large subtropical embay- 

 ment (13 years) (Hesp et al., 2004). 



Although R. sarba is typically re- 

 garded as a marine species that fre- 

 quently uses estuaries as a nursery 

 area (e.g., Wallace, 1975; Potter and 

 Hyndes, 1999; Smith and Suthers, 

 2000), it spawns in the lower Swan 

 River Estuary as well as in coastal 

 waters outside this estuary (Hesp and 

 Potter, 2003). However, this sparid 

 attains maturity later in the estuary 

 than in those nearby coastal marine 

 waters. If this indication that the on- 

 set of spawning for R. sarba in the 

 Swan River Estuary is related to the 

 attainment of higher salinities in the 

 spring, it would parallel the situation 

 recorded for the spotted seatrout (Cy- 

 noscion nebulosus) in the estuaries of 

 the Gulf of Mexico where this species 

 completes its entire life cycle ( Brown- 

 Peterson et al., 2002). 



Despite the importance and wide- 

 spread occurrence of R. sarba. and 

 the great value of fecundity data for 

 stock assessments (Hunter et al., 

 1992: Nichol and Acuna, 2001), on- 

 ly one attempt has apparently been 

 made to estimate the annual fecun- 

 dity of wild populations of this sparid 

 (El-Agamy, 1989). Although El-Aga- 

 my (1989) recognized that R. sarba 

 is a "fractional" spawner and has a 



