FISHERY BULLETIN: VOL. 80, NO. 3 



formation on natural feeding duration was taken 

 from Miller, 5 which showed that wild larvae feed 

 24 h a day but feed more intensely during crepus- 

 cular periods. Evacuation rate was set at 5 h, a 

 compromise between our estimate of 3.3 h for 

 larvae fed Artemia at 18°C and the estimate of 1 1 

 to 12 h made by McHugh and Heidinger (1977) 

 for larvae given Artemia and held at 25°C. Daily 

 caloric rations for wild larvae range from 0.646 

 cal for smaller larvae to 4.151 cal for 11.0 to 11.9 

 mm SL larvae. These rations are higher than 

 those of laboratory larvae. Except for the largest 

 cultured larvae, rations were usually one-half 

 the field larvae rations. Thus within equivalent 

 size categories wild larvae appear to have daily 

 rations substantially greater than those of cul- 

 tured larvae. Other estimates of daily rations of 

 striped bass larvae range widely. Miller (foot- 

 note 5) concluded that field-caught larvae (6.8 to 

 9.2 mm SL) consumed rations equivalent to 0.159 

 cal for rotifers or up to 2.958 cal for cladocerans. 

 Doroshev (1970) estimated daily intake of labora- 

 tory-reared larvae to be 9.704 to 29.112 cal, con- 

 sisting of Cyclops nauplii or small copepods. Our 

 average calculated daily estimates for the differ- 

 ent food concentrations for the 29-d experimental 

 period fall within Miller's estimates of wild lar- 

 vae (Table 8). 



Table 8. — Mean daily caloric rations of striped 

 bass larvae given five different food densities from 

 D-7 to D-29. 



Energy Outputs 



Our results suggest that there is compensatory 

 growth in embryos and larvae that offsets initial 

 egg size differences. The size ranges are not as 

 broad in newly hatched larvae and larvae at first 

 feeding (D-7) (seen in Table 5) as they are in the 

 eggs. Likewise, initial egg size corresponds bet- 

 ter to the size ranking of larvae at hatching age 

 than it does to larvae at feeding age. The mean 

 instantaneous growth coefficient during the 2-d 

 embryonic period was 1.872 with a coefficient of 



5 Miller, P. E., Jr. 1978. Food habit study of striped bass 

 post yolk-sac larvae. The Johns Hopkins University, Chesa- 

 peake Bay Institute, Spec. Rep. 68, Ref. 78-8. 



variation (C. V.) of 8.5% (Table 5). From hatching 

 to first feeding it was 0.647 with a decreased C.V. 

 of 7.0%, an indication of narrowing diversity. 

 Further compensatory growth was seen in tissue 

 weights and standard lengths of feeding larvae 

 (Figs. 4, 5), and convergence of sizes was seen in 

 all food concentrations above 0.10 Artemia/m\. 

 Weights were similar on D-25 and lengths on D- 

 27. In the two higher food concentrations, sizes 

 converged by D-17. Compensatory growth was 

 documented years ago in salmon fry (Hayes and 

 Armstrong 1942), so this is not necessarily 

 unique to striped bass. Theilacker (in press) 

 more recently found that growth rates of jack 

 mackerel larvae varied with egg size. 



Growth of feeding striped bass larvae was 

 clearly tied to exogenous food consumption as 

 seen in Figure 6. This relation is well established 

 in other larval fishes (O'Connell and Raymond 

 1970; Saksena and Houde 1972; Laurence 1974; 

 May 1974a; Houde 1977; Taniguchi in press). 



Growth rates of our larvae, especially those in 

 the higher food concentrations, are similar to 

 findings with other populations of striped bass 

 (Rogers et al. 1977). The most comparable study 

 (Daniel 1976) included continuous introduction 

 of Artemia for 10 d in concentrations of 0.004 to 

 0.030 nauplii/ml. Twenty-five days after hatch- 

 ing larvae grew to an average standard length of 

 8.5 mm. Fish used in the present study were 

 longer than Daniel's in the two higher food con- 

 centrations and smaller in the three lower con- 

 centrations. As in our study, Daniel's larvae also 

 grew directly in relation to food density. Tissue 

 weights of Daniel's fish fed the 0.008 and greater 

 Artemia/ml concentrations approximated those 

 of our fish fed concentrations of 0.005 and above. 

 Our larvae that fed at 5.0, however, were all 

 heavier than Daniel's larvae. Lai etal.( 1977) also 

 cultured California striped bass larvae but in 

 varying salinities. Larvae of comparable age 

 feeding on Artemia (densities unreported) were 

 similar to our larvae from the 0.50 nauplii/ml. 

 Larvae from our higher densities were larger. 



Oxygen consumption measurements varied 

 directly with size, age, and temperature. Be- 

 cause temperature was held constant in all tests, 

 age and size were the most influential factors 

 affecting oxygen consumption, and these factors 

 produced distinctive patterns. The high meta- 

 bolic rates (Qo 2 's) demonstrated by embryos and 

 newly hatched larvae were probably the results 

 of the activity accompanying hatching and of the 

 high metabolic needs associated with rapid tis- 



470 



