vided food in densities we felt would not limit 

 growth. 



Growth in standard length (SL) from the time lar- 

 vae begin feeding to age 21 d at 20° C was modeled 

 by an exponential equation. All measurements were 

 made on eggs and larvae that were preserved in 5% 

 sodium acetate buffered Formalin 1 . Volumes (V) of 

 the elliptically shaped yolk mass were calculated 

 using the formula for a prolate spheroid 



V = (n/6) lh 2 , 



where I is the length and h is the height of the yolk 

 mass (Blaxter and Hempel 1963). 



We were unable to treat the two species the same 

 in most experiments. The gulf menhaden was sub- 

 jected to a greater number of treatments than the 

 Atlantic menhaden. Experiments dealing with 

 starvation and yolk utilization rates were conducted 

 only on the gulf menhaden. In addition, the lack of 

 replications for some experiments limited the ap- 

 plication of statistical tests (e.g., ANOVA) and, as 

 a result the differences or similarities between the 

 two menhadens, should be considered tentative. 



Results and Discussion 



Based on a sample of eggs from the single spawn 

 of a group of approximately five females from each 

 species, Atlantic menhaden had significantly (P < 

 0.001) larger eggs (1.6 mm diameter, N = 20) than 

 gulf menhaden (1.3 mm diameter, N = 20). Egg 

 sizes for both these species that have been reported 

 (Houde and Fore 1973; Jones et al. 1978; Hettler 

 1984) support our observations that Atlantic men- 

 haden eggs are larger than gulf menhaden eggs. 

 Atlantic menhaden larvae measured at hatching also 

 were larger than gulf menhaden (Fig. 1) and sup- 



ports Blaxter and Hunter's (1982) view that egg size 

 greatly influences the size of larvae at hatching. 



Temperature did not affect the size at hatching 

 of gulf menhaden (Fig. 1), but the rate of yolk utiliza- 

 tion was affected by temperature and was roughly 

 2.5 times faster at the highest temperature (24 °C) 

 than at the lowest temperature (14°C) (Table 1). The 

 instantaneous rate of yolk utilization increased 

 linearly with increasing temperature (Fig. 2). The 

 volume of yolk at the onset of exogenous feeding 

 (first feeding) was approximately similar at all tem- 

 peratures (Table 1) and was not affected by temper- 

 ature (ANOVA, P = 0.13). 



The size of gulf menhaden at first feeding was in- 

 dependent of temperature (Fig. 3) (ANOVA P = 

 0.15) and, although data are limited, the size of 

 Atlantic menhaden also was independent of tem- 

 perature. The age at first feeding, however, was 

 dependent on temperature (Fig. 3). An ANCOVA 

 (log transformed ages on temperature) revealed that 

 the regression slopes were similar (P = 0.37), in- 



i- 

 < 



E 

 E 



O 



z 

 ai 



DW 



s« 



ZO 



<Z 



UjX 



14 16 18 20 22 24 



TEMPERATURE °C 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Figure 1.— The size at hatching of Atlantic gulf menhadens at dif- 

 ferent temperatures. Each point represents the mean of 10 fish. 



Table 1 .—The effects of temperature on yolk utilization of gulf menhaden. For regression equations, 

 Y = log e preserved yolk volume (mm 3 ) and X = age (d). The equations were derived from the means 

 of approximately 10 fish per sample. S is the number of samples; N is the number of larvae. 



992 



