MacFarlane and Norton: Nutntional dynamics of embryonic-stage Sebastes 



275 



Lipids were extracted from oocytes and embryos 

 by the method of Bhgh and Dyer ( 1959). Total Upids 

 were quantified by using thin layer chromatography 

 with flame ionization detection (TLC-FID) by an 

 latroscan TH-10 Mark III (MacFarlane et al., 1990; 

 MacFarlane et al., 1993). Lipids were separated into 

 steryl or wax ester, triacylglycerol, nonesterified fatty 

 acid, cholesterol, and polar lipid classes on Chro- 

 marods S-III in a solvent bath of hexane:ethyl 

 ether:formic acid at a ratio of 246:54:0.09. Quantifi- 

 cation of separated peaks by TLC-FID was accom- 

 plished by comparing peak areas to external stan- 

 dard curves for each lipid class. Cholesterol oleate, 

 triolein, oleic acid, cholesterol, and phosphatidylcho- 

 line, purchased from Sigma Chemical Co. (St. Louis, 

 MO), were used as standards. Total protein was esti- 

 mated with the Lowry method by using a bovine se- 

 rum albumin standard (Lowry et al., 1951). 



Analysis of variance (ANOVA) was employed to 

 assess variation in lipids and protein by embryo 

 maturation stage (EMS), rockfish species, or popu- 

 lation of shortbelly rockfish. Estimated concentra- 

 tions of nutrients at parturition were obtained by 

 linear regression. All analyses were performed with 

 SAS statistical software (SAS Institute, Inc., 1989). 



Lipids and protein data are presented as concen- 

 trations, mg/g wet weight. Changes in concentration 

 during embryonic development represent absolute 

 changes in the quantities of lipids and protein be- 

 cause ovarian mass remained statistically 

 constant through gestation for both species. 

 ANOVA results of the relationship between 

 GSI [gonadosomatic index = (ovary weight/ 

 body weight) x 100] and EMS were P = 0.242 

 (F= 1.396, df=59) for yellowtail rockfish and 

 P = 0.622 (F=0.243, df=202) for shortbelly 

 rockfish. During gestation, changes in organic 

 mass of ovaries were compensated by changes 

 in water concentration. Regression equations 

 for ovarian water concentration by EMS were 



Yellowtail rockfish ovarian water (mg/g) 

 = 608.5-t-8.292(£;MS), 

 [df=59, F=203.7, P<0.0001, r-=0.778] 



Shortbelly rockfish ovarian water (mg/g) 

 "=655.2h-6.860(£MS). 

 [df=172, F=782.6, P<0.0001, r^=0.821] 



Results and discussion 



There was a progressive decline in total lipid 

 =and protein during embryogenesis in yellow- 

 tail rockfish, Sebastes flavidus (Fig. 1). The 



o 

 U 



concentration of total lipid decreased from a mean of 

 149.8 mg/g in unfertilized, late vitellogenic oocytes 

 (EMS 1) to an estimated concentration of 48.4 mg/g 

 for fully formed, hatched larvae (EMS 33) at partu- 

 rition. Although no pregnant females were caught 

 with embryos at EMS 33, the goodness-of-fit (r^ value) 

 of the linear regression of lipid concentration on 

 embryo maturation stage (Table 2) suggested that 

 calculation of total lipid at parturition was valid 

 (Table 3). Similarly, protein declined from 225.9 mg/g 

 during EMS 1 to 52.1 mg/g at EMS 33 (Fig. 1; Table 3). 

 These data indicate that yellowtail rockfish embryo- 

 genesis consumed more protein than lipid for nutri- 

 tional requirements because protein concentration 

 declined 77% during development whereas total lip- 

 ids decreased 68%. From an energetic perspective, 

 however, lipid was predominantly utilized. Using 

 values for physiologically available energy density 

 of 39.6 kJ/g of lipid and 20.1 kJ/g of protein (Brett 

 and Groves, 1979), we found that the 101.4 mg lipid/g 

 embryo depleted during embryogenesis 3delded 4.02 

 kJ of energy, whereas the 173.8 mg protein/g embryo 

 yielded 3.49 kJ. The predominance of lipid as an en- 

 ergy source for viviparous reproductive development 

 in yellowtail rockfish has been demonstrated previ- 

 ously (MacFarlane et al., 1993; Norton and Mac- 

 Farlane, 1995). The consumption of yolk proteins, 

 particularly those with high molecular weights > 70 

 kDa, during embryonic maturation of yellowtail rock- 



Sebastes flavidus 



Tola! Protein 



Total Lipid 



/ 



1 6 11 16 21 26 31 



Embryo maturation stage 



Figure 1 



Total lipid and protein concentrations in oocytes and embryos by 

 embryo maturation stage (EMS) in female yellowtail rockfish, 

 Sebastes flavidus, from prefertilized oocytes (EMS 1) through the 

 yolk-reduction stage (EMS 30). Data presented as means ± SE. Mean 

 number (range) of females assayed at each EMS was 12 (9-17). See 

 Table 1 for descriptions of EMS. 



