Changes in RNA, DNA and protein contents of laboratory-reared Japanese flounder Paralichthys olivaceus during metamorphosis and settlement

Abstract

By means of biochemical analyses on an individual basis, developmental changes in nutritional status during metamorphosis and settlement were examined in laboratory-reared Japanese flounder Paralichthys olivaceus. Although whole-body DNA content increased gradually throughout metamorphosis and settlement, the RNA content generally remained constant during the late metamorphosing stage and postmetamorphic phase. Subsequently, the RNA:DNA ratio decreased drastically from the late metamorphosing stage to the postmetamorphic phase following a continuous elevation in the ratio during early and mid-metamorphosing stages. The changes in protein content coincided well with RNA content. The protein:DNA ratio also peaked at the postmetamorphic phase and decreased for several days thereafter, suggesting the occurrence of hypertrophy until the postmetamorphic phase, followed by hyperplasia. It is speculated that the nutritional status of Japanese flounder becomes lower when associated with entry to the final phase of metamorphosis and/or settlement at which feeding habits drastically change. Poor nutritional status of the newly settled juveniles may increase their vulnerability to predators in the nursery ground.