Changes in RNA/DNA ratio and growth of slime flounder, Microstomus achne, larvae until metamorphosis

Abstract

Summary Understanding the nutritional condition and survival of fish larvae is of primary importance in mass larva culture because intensive mortality is concentrated during the larval period. In order to estimate growth and nutritional status based on biochemical indices of slime flounder, Microstomus achne, larvae reared under starved and fed conditions in the hatchery for 58 days and the changes of RNA, DNA, and protein contents were described with the progress of growth and developmental. DNA contents increased gradually throughout the experimental period until 12 and 58 days post-hatching (DPH) in starved and fed groups respectively. Although they fluctuated and decreased around 12 and 46 DPH, the RNA contents of the fed group increased gradually after hatching; however, in the starved group, they decreased after yolk absorption and 7 DPH. Subsequently, the RNA/DNA ratios in the starved group remained constant until 6 DPH and then decreased rapidly. In the fed group, this decreased slightly from hatching to 14 DPH, then increased gradually until the end of the experiment, except at the lower level of around 46 DPH. Namely, temperature shocks (around 14 DPH) and the dramatic changes in body shape (around 46 DPH) were accompanied by the decrease of the RNA/DNA ratios. Total protein/DNA in both groups decreased rapidly during yolk absorption 0–7 DPH, then decreased continuously until death in the starved group; in the fed group total protein/DNA increased again with feeding. It is suggested that the changes in these biochemical values reflect yolk absorption, feeding, morphogenetic changes, growth, and environmental conditions.