IMPROVEMENTS IN THE FLUOROMETRIC-DETERMINATION OF THE RNA AND DNA CONTENT OF INDIVIDUAL MARINE FISH LARVAE

The RNA/DNA ratio is a useful indicator of the nutritional condition o f fish larvae. The presented analytical procedure is an improvement of Clemmesen's (Meeresforschung 32: 134-143, 1988) methodology which inv olves purification of fish larvae tissue homogenates and subsequent fl uorescence-photometric measurements using specific nucleic acid dyes. The modifications concern the homogenization and nucleic acid extracti on procedures. A 'shaking mill' was compared to a potter Elvehjem micr ohomogenizer and a reduction in the washing and purification steps was achieved. Treatment of samples with ribonuclease A and subsequent flu orescence measurement using ethidium bromide was given preference comp ared to the DNA-bisbenzimidazole determinations due to problems arisin g from high self-fluorescence of the samples and the influence of 'que nching' substances disturbing the DNA-bisbenzimidazole determinations. Different RNase concentrations and their influences on RNA and DNA we re checked. Recovery rates of standard RNA and DNA 'spikes' were deter mined. Fish larvae samples were analysed with the previous and the imp roved modified procedure and a correction factor to compare results me asured with the 2 procedures was calculated. With the presented method the physiological condition of individual larvae and the amount of va riability can be determined.