FISHERY BULLETIN: VOL. 84, NO. 4 



14 



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 £ 



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10 



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© SB 

 a WBX 

 A WPX 



I ±2 SE 



9 13 17 20 23 

 Days after Hatching 



27 30 



Figure 3.— Mean standard lengths (±2 standard errors) of striped 

 bass (SB), striped bass x white bass (WBX), and striped bass x 

 white perch (WPX) larvae on seven dates in 2 m 3 enclosure ex- 

 periments, Manning Hatchery pond. 



tained for Morone larvae at low Artemia concentra- 

 tions, if those concentrations are maintained at the 

 nominal levels. Our laboratory survival rates at low 

 food levels were higher than those reported for 

 striped bass larvae in the literature (e.g., Doroshev 

 1970; Miller 1978; Rogers and Westin 1981; Eld- 

 ridge et al. 1981, 1982), which generally had in- 

 dicated that nominal Artemia concentrations nearly 

 an order of magnitude higher than 500 L _1 were 

 required to obtain high survival rates. 



The laboratory and pond enclosure methods to 

 assess striped bass and hybrid larvae performance 

 differed in many respects and could have influenced 

 results. Besides great differences in enclosed vol- 

 umes (36 L vs. 2 m 3 ), environmental factors and 

 foods differed. Laboratory experiments were run at 

 19.0 °C and 3%o salinity, because low salinities are 

 known to improve striped bass larvae survival (Bonn 

 et al. 1976; Kerby et al. 1983). Temperature in- 

 creased from 18.5° to 22.5°C in the Manning Hatch- 

 ery freshwater pond during the 3-wk experiment. 

 The laboratory-reared fish were fed only Artemia 

 nauplii at controlled concentrations while enclosure 

 fish had a variable zooplankton diet. 



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O) 



"3 



20 



10 



© SB 

 a WBX 

 a WPX 



I ±2 SE 



9 13 17 20 23 

 Days after Hatching 



27 30 



Figure 4.— Mean wet weights (±2 standard errors) of striped bass 

 (SB), striped bass x white bass (WBX), and striped bass x white 

 perch (WPX) larvae on seven dates in 2 m 3 enclosure experiments, 

 Manning Hatchery pond. 



Survival of all larvae was lower in the pond en- 

 closures than in the laboratory tanks (Tables 1, 4). 

 White bass hybrids had the lowest mean survival 

 rate in the laboratory but they survived as well as 

 striped bass and white perch hybrids in the pond 

 enclosures. At the relatively high 500 L _1 Artemia 

 level laboratory-reared striped bass larvae were 

 longer and heavier than either of the hybrids at 30 

 d after hatching. In the pond enclosures no signifi- 

 cant differences in mean lengths or weights among 

 the three types of larvae were detected at 30 d. The 

 weight-length relationship of pond enclosure, white 

 bass hybrid larvae had a relatively high exponen- 

 tial coefficient, indicating that they were heavier at 

 a given length than the other types of larvae. Mean 

 weights of both hybrids at 30 d were considerably 

 heavier in the pond enclosures than in the labora- 

 tory tanks. Relatively great size variability in the 



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