APPLICATION OF RNA - DNA RATIOS TO EVALUATE THE CONDITION AND GROWTH OF LARVAL AND JUVENILE RED DRUM (SCIAENOPS-OCELLATUS)

RNA:DNA ratios in individual red drum (Sciaenops ocellatus) were measu red in laboratory-reared larvae and juveniles (6-20 mm standard length ; age 16-40 days) to assess the effects of growth, starvation, and die l periodicity on biochemical condition. RNA:DNA ratios were correlated positively with both absolute (mm day(-1)) and instantaneous (% day(- 1)) growth rates. The effect of starvation was evaluated daily over 5 day periods at three ontogenetic stages (20, 30, and 40 days). Signifi cant differences in RNA:DNA ratios of fed and starved larvae were obse rved and changes in biochemical condition were detected statistically within 1 to 2 days of food deprivation. RNA:DNA ratios decreased conti nuously over the entire 5 day starvation period, with relative reducti ons in RNA:DNA ratios decreasing with increasing age. Diel variations in RNA:DNA ratios were investigated in controlled (constant) and natur al (cyclical) temperature environments over a 48 h period. RNA:DNA rat ios were highest during daytime periods (0800, 1200, 1600, 2000 hours) and markedly reduced at night (0000, 0400 hours). Since RNA:DNA ratio s from controlled and natural temperature treatments did not differ si gnificantly, cyclical variations in temperature did not appear respons ible for diel variations in biochemical condition Findings from this s tudy support the use of nucleic acids as reliable indices of growth an d condition and suggest that RNA:DNA ratios are potentially suitable m easures to assess the condition of wild-caught S. ocellatus.