Feeding larvae of winter flounder Pseudopleuronectes americanus (Walbaum) with live prey or microencapsulated diet: linear growth and protein, RNA and DNA content

A commercial microencapsulated diet was used as a total or partial replacem ent of live prey for feeding larvae of winter flounder Pseudopleuronectes a mericanus (Walbaum), a potential alternative finfish species for coldwater marine aquaculture. Growth performance (morphometric measurements and bioch emical composition) and nutritional condition (RNA/DNA ratios) of larvae fe d live prey (Brachionus plicatilis Muller), a microencapsulated diet or a m ixed diet of live prey and microcapsules were compared. Newly hatched larva e were unable to digest microencapsulated diet; live prey at initial feedin g was required for their survival and growth. Larvae offered a mixed diet s howed slower growth than larvae fed exclusively with live prey. However, at the onset of stomach differentiation, RNA/DNA ratios (indicators of protei n synthesis potential) of the larvae fed both diets became similar. We sugg est that, at that stage (size 5.5-6.3 mm), enzymatic activity had developed enough to allow digestion of inert food. As the RNA/DNA ratio is a good in dicator of nutritional condition, it appears to be an interesting tool for the assessment of diet adequacy in marine larval feeding technology.