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 lined 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 growth rates at 100 and 50 per liter nauplii 
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 mortahty at low prey levels, the indirect effects of 
increased time of exposure to predators and possible enviornmental 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 metabolism. 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 
jug. Specific rations (jug consumed per jug larva x 100) decreased from nearly 
183 
