HOUDE and LUBBERS: SURVIVAL AND GROWTH OF STRIPED BASS 



Zooplankton Densities at Cedarville 

 Inside Enclosures 



1000 



17 20 23 



Days after Hatching 



Figure 5.— Mean densities of copepods and cladocerans inside and outside of 

 the 2 m 3 enclosures used for striped bass and hybrid larvae experiments in the 

 Manning Hatchery pond. 



enclosures may have resulted in part from canni- 

 balism and consumption of chironomids by some lar- 

 vae, promoting their relatively rapid growth. 



Although mean weights and lengths of 30-d-old 

 striped bass and the two hybrids from the pond 

 enclosures did not differ, the instantaneous rate of 

 growth in weight of striped bass larvae was signifi- 

 cantly lower than that of either hybrid (Table 4E). 

 Had the enclosure experiments proceeded for a few 

 more days the hybrids would have attained larger 

 size than the striped bass. For example, at 35 d after 

 hatching the striped bass would have weighed 20 

 mg less than either hybrid. The heterotic effect may 

 begin to express itself at approximately 1 mo of age. 

 Alternatively, the freshwater environment, increas- 

 ing temperatures, and the prey available in the pond 

 may have selectively favored growth of hybrids dur- 

 ing the last few days of the experiment. 



If 30-d-old fry are to be produced for stocking, 

 there is no apparent immediate advantage to rear 

 hybrids rather than striped bass. Our laboratory and 

 pond enclosure studies did not demonstrate advan- 



tages in survival or production of hybrids. The pond 

 enclosure results did suggest that hybrids may begin 

 to achieve an advantage in growth rates just prior 

 to 1 mo of age. Important questions about compar- 

 ative energetics, nutrition, and genetics still remain 

 to be answered to understand the biology of larval 

 M. saxatilis or its hybrids and the consequences of 

 their possible release into natural systems such as 

 Chesapeake Bay. 



ACKNOWLEDGMENTS 



The research was supported by contracts F26-82- 

 003 and F31-83-008 from the Maryland Department 

 of Natural Resources, Tidewater Administration, 

 Tidal Fisheries Division. Assistance in the labora- 

 tory was provided by H. Hornick, W. Roosenburg, 

 and V. Saksena. Larvae were supplied by the Mary- 

 land DNR Manning Hatchery at Cedarville. The 

 assistance of DNR personnel, particularly M. 

 Beaven, H. King, and J. Stringer, is gratefully 

 acknowledged. We appreciate the critiques of early 



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