bream at 50, 100 and 500 per liter copepod nauplii concentrations; they were 

 16, 17 and 25 percent per day for bay anchovy at 50, 100 and 1000 per liter 

 nauplii concentrations; but, lower rates of 7, 9 and 17 percent were obtained 

 for hned soles at 50, 100 and 1000 per liter nauplii concentrations. Depending 

 on prey concentration, the length of the larval stage can be highly variable. In 

 the case of sea bream, specific grov^h rates at 100 and 50 per liter naupHi 

 concentrations indicate that duration of the larval stage at those prey levels 

 could be 1.4 to 1 .7 times as long as at the 500 per liter level. Even if starvation 

 was not a direct cause of mortality at low prey levels, the indirect effects of 

 increased time of exposure to predators and possible enviommental stresses 

 during the larval stage, must have important consequences on the numbers that 

 eventually metamorphose. 



The density of prey, expressed as numbers per liter, provides a useful 

 measure of availability of prey for capture by larvae, but does not necessarily 

 provide a measure of energy available for growth and metabolism. Energy 

 available is a function of prey density, prey size, and the ability of larvae to 

 ingest particular prey, which is related to mouth size in many instances (10, 

 90). The kinds of prey also could influence the availability of energy, either 

 through differential ability of prey to escape capture by larvae, or through 

 differences in caloric content of prey. Few studies concerned with marine fish 

 larvae have taken a bioenergetic approach to examine nutritional requirements. 

 Such studies can provide the means to estimate amounts of ingested energy 

 used for growth and metaboHsm. Estimates of required food intake, specific 

 ration, growth efficiency and the critical minimum prey level all can be 

 determined on a caloric basis using this method. When used in conjunction 

 with studies on feeding by larvae in relative to prey concentration, valuable 

 insight into nutritional requirements and feeding dynamics can be obtained. 

 Recent work by Laurence (60) on winter flounder larvae is the best example of 

 the use of a bioenergetic model for marine fish larvae. 



The winter flounder larvae model (60) predicted critical food 

 concentrations in the range 2.1-5.7 cal per liter, corresponding to 300-800 

 copepod nauplii per liter. Highest prey concentrations were required by 

 newly-feeding larvae, suggesting that food was most critical at that time. 

 Smallest larvae required most of the daylight period to obtain a minimum 

 ration. Relatively high metabolic energy demands were made by the smallest 

 larvae, reflecting their low efficiency in capturing food. Metabolic demands 

 were lowest at high prey concentrations because larvae expended less energy in 

 searching when food was readily available. Thus, for winter flounder larvae it 

 appears that food consumption needs to be higher at low prey concentrations 

 than at high prey concentrations. Estimated minimum consumption ranged 

 from 18-230 nauplii per day over a range of larval dry weights from 10-1000 

 /xg. Specific rations (/ng consumed per /ig larva x 100) decreased from nearly 



183 



