300 percent for newly-feeding larvae to 27-31 percent tor the smallest larval 
stages (10-75 jug), and continued to increase slowly for older larvae, ranging 
from about 18-33 percent for metamorphosed individuals. Laurence (60) 
predicted a continuous decrease in growth efficiency as prey concentrations 
were decreased, but so few values of growth efficiency are available for fish 
larvae that it is not possible to say whether this relationship will hold for other 
species. 
Some valuable insight into feeding by marine fish larvae recently has been 
gained by combining results of bioenergetic studies on larvae with studies on 
feeding behavior and feeding ability of larvae. Blaxter and Staines (23) 
estimated swimming ability and feeding efficiency of herring, plaice, pilchard 
Sardina pilchardus , and sole Solea solea larvae. From their estimates they 
calculated the volume of water that could be effectively searched by larvae 
when they initiated feeding, and at sizes up to metamorphosis. Because 
swimming distances and volumes searched per unit time increased rapidly as 
larvae grew, larvae presumably needed higher prey concentrations during the 
youngest feeding stages. A similar approach was used by Rosenthal and Hempel 
(82), who in addition estimated the digestion time for herring larvae. They 
were then able to calculate the daily ration and required densities of prey 
(Artemia nauplii) for herring larvae at the end of the yolk-sac stage (10-11 mm) 
and at 13-14 mm length. Estimated ration was 40 Artemia nauplii per day at 
10-11 mm and 50 per day at 13-14 mm. Required Artemia concentrations for 
larvae to obtain the rations at each of those length-classes were 4 to 42, and 2 
to 25 per liter, respectively. Hunter (46) further extended the method by 
incorporating metabolic demands of larvae, and caloric values of prey (the 
rotifer Brachionus plicatilis and the dinoflagellate Gymnodinium splendens) 
into the prediction of food requirements. He concluded that first feeding 
northern anchovy larvae required 105 rotifers per liter or their caloric 
equivalents (e.g. 1785 Gymnodinium per liter) to just meet metabolic 
demands. Larvae at 10 days (5.9 mm) required only 34 rotifers per liter. In all 
of the examples, the relatively poor swimming ability and the low prey capture 
efficiency of first feeding larvae were demonstrated. This implies, as did 
Laurence’s study (60), that food concentration is most critical at the first 
feeding stage and, when low, could be a significant cause of larval mortality in 
the sea. 
It is possible to make many conclusions about larval food requirements 
based on dry weights of larvae, dry weights of prey, prey selection by larvae, 
digestion time, and estimates of the caloric values of the prey (cal/g ash free). 
Using these methods, Stepien (92) showed how feeding rates, specific rations 
and growth efficiency of sea bream larvae varied in relation to larval age, and to 
temperature for a single prey concentration. At 1000 copepod nauplii per liter, 
feeding rates for first feeding larvae (2-3 days after hatching) varied from 7.2 
184 
