Growth and developmental patterns based on RNA, DNA and protein content during early ontogeny of laboratory-reared greater amberjack Seriola dumerili

抄録

Nucleic acid and protein-based biochemical indices of fish larvae and juveniles have been analysed to evaluate their growth and development. However, little is known about the ontogenetic changes in these biochemical indices in relation to individual fish body sizes. In the present study, larvae and juveniles of laboratory-reared greater amberjack Seriola dumerili, from 1 to 25 days post-hatching, were used as a model organism to perform piecewise regression analyses between log-transformed values of total length (TL) and RNA (an index of protein synthesis capacity), DNA (an index of cell number) and protein content (an index of absolute growth), as well as those between TL and RNA/DNA, RNA/protein and protein/DNA ratio of individual fish. The RNA/DNA ratio decreased during the prelarval stage; after that, it linearly increased, suggesting a steady increase in protein synthesis capacity per cell from the preflexion stage onwards. The protein content exhibited positive allometric growth, while the RNA/protein ratio, an index of overall protein synthesis capacity, slowly declined after the transition from the preflexion to flexion stages, indicating that the efficiency of retention of newly synthesized proteins might have improved. Meanwhile, the protein/DNA ratio, which is a measure of cell size, decreased during the prelarval, preflexion and early flexion stages, reflecting hyperplasia with positive allometric growth of DNA content and low protein increment, and hypertrophy occurred after the early flexion stage, reflecting the negative allometric growth of DNA content and positive allometric growth of protein content. The biochemical synthesis appeared to enter a stable growth phase from the mid-flexion stage, accompanying the progress of morphological, physiological and behavioural development in greater amberjack larvae. Therefore, piecewise regression analyses could detect changes in growth and developmental patterns based on nucleic acid and protein content during the early ontogeny of fish species.