ENERGETICS OF LARVAL RED DRUM, SCIAENOPS-OCELLATUS .2. GROWTH AND BIOCHEMICAL INDICATORS

The effects of ration level and temperature on growth were determined for larval red drum, Sciaenops ocellatus, during its first two weeks o f life. Larvae were raised in the laboratory at 20 degrees C at a rati on level of 5.0 prey/mL, at 25 degrees C at ration levels of 0, 0.1, 1 .0, and 5.0 prey/mL, and in growout ponds at 25 degrees C and 32 degre es C and at ration levels of 4-6 prey/mL. Growth was measured as stand ard length, wet mass, and dry mass. Proximate (water, ash, protein, an d lipid) and elemental(C, N) composition was determined at larval ages of 0, 2, 4, 6, 10, and 14 d to provide caloric values for the growing larvae and to examine the relative importance of protein and lipid du ring tissue deposition in the very early life history of these larvae. Biochemical indicators of growth, RNA-DNA ratio, and activity of the metabolic enzyme lactate dehydrogenase (LDH) were examined in larvae r eared at all temperature and ration combinations. The effectiveness of the biochemical indicators as proxies for growth was assessed by comp aring the directly measured growth rates with RNA:DNA levels and LDH a ctivity. Larvae fed a ration of 1.0 prey/mL or less did not survive pa st the age of eight days. Growth rate increased with increasing temper ature, reaching a maximum of 60% body mass/d in growout ponds at 32 de grees C. Protein level (percent ash free dry mass: %AFDM) increased wi th increasing age in all treatments where individuals exhibited positi ve growth, whereas lipid (%AFDM) showed a concomitant decline. Nitroge n (%AFDM) and carbon (%AFDM) varied directly with protein and lipid co ntents, respectively. Biochemical indicators of growth showed a signif icant correlation with growth rate. However, the character of the corr elation changed with temperature. RNA-DNA ratios and enzymic activitie s were lower at higher temperatures for equivalent growth rates. Intro duction of a temperature term into multiple regression equations impro ved the relation between growth and the biochemical proxies. LDH activ ity scaled with the size of larvae, whereas RNA:DNA showed no signific ant relation with size.