692 



Fishery Bulletin 92(4). 1994 



opment. We believe that any putative increase in the 

 proteinaceous yolk as oocytes ripened was not de- 

 tectable by the methods used in this study because 

 the follicles were also increasing in size as oocytes 

 matured. That is, protein concentration was rela- 

 tively stable because structural protein (follicles, etc.) 

 contributed far more to the total protein concentra- 

 tion than did yolk proteins. 



Lipid was the second most abundant component 

 but the levels changed from stage to stage, ranging 

 from 21 to 41%. The fluctuations in lipid concentra- 

 tion during ovarian maturation can be explained by 

 the increasing amount of lipid yolk reserves that are 

 deposited as oocytes mature from stages 1 to 3 fol- 

 lowed by the subsequent loss of ripe oocytes from the 

 ovary after ovulation and spawning. 



Carbohydrate was the least abundant component 

 (3^i7( ) of cobia ovaries and ash ranked third ( 6-20% ). 

 Boulekbache (1981) noted that the enzymes of car- 

 bohydrate metabolism increased in activity during 

 oogenesis. Carbohydrate concentration, therefore, 

 may be low due to constant catabolism. In the present 

 study, it is not known whether carbohydrate was con- 

 stantly being catabolized and replaced, or whether 

 concentrations were low. In most fish, however, car- 

 bohydrate is not readily available for use until after 

 fertilization occurs (Boulekbache, 1981). The trend 

 in ash concentrations was the inverse of lipid con- 

 centrations; that is, ash concentration declined when 

 the lipid concentration increased and vice versa. 



Results of biochemical analysis of ripe ovaries from 

 similar studies using other species offish are given in 

 Table 3. Protein was the major component of ripe ova- 

 ries followed by lipid, ash, and carbohydrate for cobia, 

 Rachycentron canadum (this study), striped mullet, 

 Mugil cephalus (Lu et al., 1979), plaice, Pleuronectes 

 platessa < Dawson and Grimm, 1980), and Atlantic cod, 

 Gadus morhua (Kjesbu et al., 1991). The primary dif- 



o 



2 



o 



< 



r- 



o 



O 



z 

 o 

 u 



4 V 2' 

 DEVELOPMENTAL STAGE 



Jan Mar Apr May Jul Aug Sep 



MONTH 



Figure 4 



(A) Gonosomatic index (mean ± standard 

 deviation) of cobia, Rachycentron cana- 

 dum, in relation to stage of ovarian devel- 

 opment. (B) Gonosomatic index (mean ± 

 standard deviation) of cobia in relation to 

 month of capture. Numbers above error 

 bars are sample sizes. 



ferences among the four species of fish were the rela- 

 tive proportions of protein and lipid. Ripe cod ovaries 

 had less than half the amount of lipid than either mul- 

 let or cobia; cobia ovaries had -1.1 times more lipid 

 than mullet ovaries. Only for the anabantid Tricho- 

 gaster pectoralis (Hails, 1983) was lipid the major com- 

 ponent of ripe ovaries. 



Since lipid is the most efficiently stored energy 

 reserve, supplying 9.5 cal/mg, whereas protein lib- 

 erates 5.7 cal/mg and carbohydrate 4.1 cal/mg (Crisp, 

 1984), one might expect fish eggs to have large 

 amounts of lipid to supply the energy needed for 

 growth and metabolism during embryogenesis and 



