reported by Houde (45). O'Connell and Raymond (73) estimated that more 

 than 1000 nauplii per Uter were required by northern anchovy larvae. Haddock 

 Melanogrammus aeglefinus, larvae required 500-3000 per liter (58) and winter 

 flounder, Pseudopleuronectes americanus , required 300-3000 per liter (60). It 

 is possible that some reported prey concentrations required by larvae could be 

 too high. Saksena and Houde (84) needed 1500-2000 nauplii per liter to 

 successfully rear about 10 percent of bay anchovy larvae, but more recent 

 experiments, with refined culture methods (45), have demonstrated that only 

 100 nauplii per liter are necessary to attain that survival rate. In some research, 

 such as toxicological studies to determine effects of pollutants on larval 

 survival, potential survival rates higher than 10 percent are required. For those 

 studies, copepod nauplii concentrations of 1000 per liter or higher should be 

 routinely employed (44, 45) (Table 13-1). 



For six cases where copepod nauplii were fed to similar-sized larvae, the 

 relationship between percent survival and nauplii concentration can be 

 compared (Table 13-1). Haddock larvae had the highest required prey 

 concentration, more than 2000 nauplii per Hter being required for 10 percent 

 survival. Winter flounder and northern anchovy larvae had an expected survival 

 of 10 percent when naupUi were available at approximately 1600 and 1000 per 

 liter, respectively. But, bay anchovy and lined sole required only about 100 

 nauplii per liter and sea bream needed less than 50 per liter to attain 10 percent 

 survival. All of these species consume prey of similar types and sizes; the 

 differences in requirements among species have not been explained. 

 Temperature may play a role because the three species with lowest required 

 prey concentrations were reared at 26-28°C, while the three with higher 

 requirements were reared at 7-1 7°C. If searching ability and capture efficiency 

 are enhanced at higher temperatures, required prey concentrations may 

 decrease accordingly. 



Rotifers, Brachionus plicatilis, are often used at high densities by 

 aquaculturists to successfully rear fish larvae, but the minimum concentration 

 required by larvae usually has not been determined. Hunter (46) estimated that 

 105 rotifers per liter were required by newly-feeding northern anchovy larvae 

 to meet metabolic demands, a number that must be exceeded for larvae to 

 grow. Lined sole larvae required from 60-120 rotifers per Uter for 10 percent 

 survival to metamorphosis (Houde, unpublished data). 



Concentrations of microzooplankton in marine waters are not frequently 

 reported, but when suitable collection techniques have been used observed, 

 concentrations often are in the ranges of required prey densities determined in 

 the laboratory (Table 13-2). Concentrations of suitable prey are exceptionally 

 low in oceanic waters compared to coastal waters, and larval survival may 

 depend upon the occurrence of relatively dense prey patches in oceanic areas. 



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