Metabolism of larval turbot Scophthalmus maximus (L.) and uptake of amino acids from seawater studied by autoradiographic and radiochemical methods

Abstract

The ability of larval turbot Scophthalmus maximus (L.) to ingest labelled 14C-alanine seawater during their yolk-sac stages was investigated by means of autoradiographic and microscopic methods. Autoradiograms showed that after 24 h of exposure to 14C-alanine virtually all of the label was located in the intestinal lumen. Larval metabolism was estimated by measuring changes in dry wt, RNA:DNA ratio and C:N ratio. Dry wt decreased by ≈20% during yolk-sac absorption at 14°C and 20‰. No significant difference was observed in the RNA:DNA ratio in the larval body during this period. The C:N ratio decreased during the study. Catabolic and anabolic metabolism of the assimilated labelled amino acid was evaluated by measuring the production of 14CO 2 and the incorporation of radioactivity into molecules insoluble in TCA. Yolk-sac larvae were incubated for 24 h in labelled 14C-alanine seawater and then transferred to unlabelled media; release of labelled CO 2 by the larvae was low, but the amount of tracer incorporated into the TCA-insoluble fraction of the larval tissues was large. The data strongly suggest drinking activity and a concomitant intake of amino acids in turbot larvae during the yolk-sac stage. The results indicate that the labelled amino acid presumably contributes to the general metabolism of the larvae.