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 of life. Larvae were raised in the laboratory at 20 degrees C at a ration 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 degrees C and at ration levels of 4-6 prey/mL. Growth was measured as standard length, wet mass, and dry mass. Proximate (water, ash, protein, and 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 during 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 reared at all temperature and ration combinations. The effectiveness of the biochemical indicators as proxies for growth was assessed by comparing the directly measured growth rates with RNA:DNA levels and LDH activity. Larvae fed a ration of 1.0 prey/mL or less did not survive past the age of eight days. Growth rate increased with increasing temperature, reaching a maximum of 60% body mass/d in growout ponds at 32 degrees C. Protein level (percent ash free dry mass: %AFDM) increased with increasing age in all treatments where individuals exhibited positive growth, whereas lipid (%AFDM) showed a concomitant decline. Nitrogen (%AFDM) and carbon (%AFDM) varied directly with protein and lipid contents, respectively. Biochemical indicators of growth showed a significant correlation with growth rate. However, the character of the correlation changed with temperature. RNA-DNA ratios and enzymic activities were lower at higher temperatures for equivalent growth rates. Introduction of a temperature term into multiple regression equations improved the relation between growth and the biochemical proxies. LDH activity scaled with the size of larvae, whereas RNA:DNA showed no significant relation with size.