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Fishery Bulletin 104(2) 



gonad (qualitative methods), somatic indices (e.g., GSI, 

 HIS, and Kn), or evolution of oocyte diameter (quan- 

 titative methods) (or all four methods) are commonly 

 applied. Many authors have disagreed about their ap- 

 plications and biological interpretation (De Vlaming et 

 al., 1982; Wootton, 1990; Shapiro et al., 1993; Sadovy, 

 1996; Karlou-Riga and Economidis, 1997). Our results 

 demonstrate that the GSI indicates only the spawning 

 peak and not the presence of batch or multiple spawn- 

 ing within the species; and the HSI and Kn do not 

 exhibit a clear trend throughout the year. Normally, 

 variations of these indices (HSI and Kn) imply energy 

 storage for reproduction (Hoar et al., 1983; N'Da and 

 Deniel, 1993). However, S. atricauda does not require 

 such storage because feeding activity is not altered 

 during the reproductive period (Morato et al., 2000). 

 Oocyte diameter presents a trend similar to that of GSI, 

 although its biological interpretation is different. The 

 oocyte may begin the vitellogenesis phase and there 



□ March ■July 



Oocyte diameter (microns) 



Figure 5 



Oocyte size-frequency distributions l25-iim intervals) for blacktail 

 comber tSerraus atricauda) ovaries from the Canary Islands. 



may be no significant increase in gonad weight. Conse- 

 quently. GSI values do not necessarily change signifi- 

 cantly when the spawning period has begun. Thus, the 

 quantitative indices (GSI, HSI, Kn) show the general 

 trend of the population, whereas the oocyte diameter 

 provides information about the population as a whole, 

 as well as at the individual level. 



The analysis of qualitative and quantitative data in 

 S. atricauda seems to indicate that spawning takes 

 place throughout the year, although the general popu- 

 lation spawns between March and July. In the Canary 

 Islands, other members of the genus spawn over long 

 periods: eight months in S. cabrilla and nine months in 

 S. scriba (Garcia-Diaz et al., 1997; Garcia-Diaz 2003). 

 These three species have the longest spawning season of 

 all fish studied in the Canaries, although they are also 

 the only species whose reproductive patterns have been 

 analyzed with histological procedures. Nevertheless, 

 environmental or biological factors (or both) must be 

 related to this extended spawning period. 

 To estimate spawning frequency, the hy- 

 drated oocyte method is less time consum- 

 ing but the POP method is better because 

 the spatial and temporal distribution of the 

 postovulatory follicle structures is not con- 

 tinuous (Hunter and Goldberg, 1980). Re- 

 productive potential measured as potential 

 annual fecundity has not been addressed 

 in any species of the genus Serranus with 

 the POP method to date. It is true that this 

 fecundity must be considered as a rough 

 estimation because the spawning frequency 

 was a preliminary estimation because of 

 the scarce number of individuals in sam- 

 pling months. Siau and Bouian (1994) cal- 

 culated the total fecundity in S. cabrilla 

 and S. scriba, considering all the vitel- 

 logenesis oocytes. Their method has been 

 widely rejected because it is valid only for 



16 

 14 - 

 12 

 10 



8- 



6 



4 



2 







20 22 24 26 28 30 32 34 36 38 40 42 



Total length (cm) 



100 200 300 400 500 600 700 800 900 1000 



Total weight (g) 



100 200 300 400 500 600 700 800 900 



Gutted weight (g) 



Figure 6 



Relationships between potential annual fecundity and total length (A), total weight (B), and gutted weight (C) for black- 

 tail comber (^Serranus atricauda) from the Canary Islands. 



