Investigation of the RNA:DNA ratios of laboratory reared and field caught larval red drum (Sciaenops ocellatus)




Drescher, Kristen Croll

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The purpose of this study was to determine the nutritional condition of naturally occurring planktonic red drum larvae using measurements of RNA:DNA ratios. The RNA:DNA ratios of red drum larvae sampled in a Texas tidal inlet during fall 1994, were calibrated with data from laboratory studies of fed and starved red drum. Data from laboratory studies showed RNA:DNA ratios of starved larvae to be consistently lower than well fed larvae. When compared to the laboratory data, RNA:DNA ratios of field caught red drum larvae ranged from values associated with starved laboratory larvae to values greater than those obtained for fed larvae. In order to account for some of the variance and to identify factors other than food availability that may have affected the RNA:DNA ratio of field caught specimens, additional laboratory studies investigated the effects of different handling techniques on the RNA:DNA ratio. Modifications in sample handling (time of day collected, variable time intervals postmortem at room temperature and variable freezer storage intervals) did not alter the RNA:DNA ratio in laboratory studies. Variance within field caught fish was attributed to varying nutritional condition with 42% of the natural population of red drum larvae experiencing some degree of food deprivation