Ontogenetic changes in nucleic acid, protein contents, and growth of larval and juvenile Japanese flounder


Abstract: In order to estimate relationships among growth potential and biochemical indicators of Japanese flounder, RNA and DNA as well as protein indices were measured from 5 days after hatching (DAH) to 45 DAH. Results showed that the RNA/DNA ratio and protein/DNA ratio had obvious relations with instantaneous growth rate (GM) and length-based instantaneous growth rate (GL) during the premetamorphic period. Significant negative correlations among protein/DNA ratio and GM and GL were then observed during metamorphosis. During the postmetamorphic phase, the RNA/DNA ratio was positively correlated with GM and GL. Data indicated that body growth of Japanese flounder is mostly hyperplastic before 20 DAH, hypertrophic until 27 DAH, and hyperplastic until the end. In order to investigate the effect of diel periodicity on RNA/DNA ratio in larvae of the fed and starved groups, an experiment was conducted for 2 days. Results showed that the average RNA/DNA ratio in the daytime was higher than that in the dark and the ratio in fed larvae was higher compared with that in starved ones. In order to examine starvation effect on RNA/DNA ratio, experiments were conducted from 20 DAH to 27 DAH. Juveniles were divided into five groups: a fed group and groups starved 1, 2, 3, and 4 days followed by refeeding. Results showed that the RNA/DNA ratio increased in the fed group and declined continuously in the starved group. After refeeding, the recovery of the RNA/DNA ratio was observed for 1-day, 2-day, and 3-day starved treatments but was not found for the 4-day starved treatment.

Keywords: Flat fishes, growth rate, RNA/DNA ratio, diel variation, starvation

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