Application of RNA: DNA ratios to evaluate the condition and growth of larval and juvenile red drum (Sciaenops ocellatus)
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abstract
RNA:DNA ratios in individual red drum (Sciaenops ocellatus) were measured in laboratory-reared larvae and juveniles (6-20 mm standard length; age 16-40 days) to assess the effects of growth, starvation, and diel 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). Significant differences in RNA:DNA ratios of fed and starved larvae were observed and changes in biochemical condition were detected statistically within 1 to 2 days of food deprivation. RNA:DNA ratios decreased continuously over the entire 5 day starvation period, with relative reductions in RNA : DNA ratios decreasing with increasing age. Diel variations in RNA : DNA ratios were investigated in controlled (constant) and natural (cyclical) temperature environments over a 48 h period. RNA: DNA ratios were highest during daytime periods (0800, 1200, 1600, 2000 hours) and markedly reduced at night (0000, 0400 hours). Since RNA: DNA ratios from controlled and natural temperature treatments did not differ significantly, cyclical variations in temperature did not appear responsible for diel variations in biochemical condition. Findings from this study support the use of nucleic acids as reliable indices of growth and condition and suggest that RNA: DNA ratios are potentially suitable measures to assess the condition of wild-caught S. ocellatus.
