RNA/DNA ratio to assess the growth performance in postlarvae of the pearl oyster Pinctada fucata (Gould, 1850)

•RNA/DNA ratio was an accurate and responsive indicator to evaluate growth of Pinctada fucata postlarvae.•Algal concentration was the most important parameter in influencing RNA/DNA ratio, followed by temperature.•The culture conditions for optimal RNA/DNA ratio were the same as those for optimal growth of P. fucata postlarvae.•Interactions among temperature, algal concentration and stocking density were not synergistic. RNA/DNA ratio (RDR) has been reported to be a feasible biochemical indicator for measuring the growth of numerous aquatic animal species. Nevertheless, its applicability has not been investigated to date in the pearl oyster Pinctada fucata (Gould, 1850). A laboratory experiment was undertaken to determine the relationship between RDR and growth rate in P. fucata postlarvae. The face-centered central composite design was used with three important factors (temperature, algal concentration and stocking density) simultaneously varied to produce a variety of growth rates. Temperature ranged between 18 and 34 °C, algal concentration between 5 and 100 cells μL―1, stocking density between 0.2 and 2.5 in.. mL―1. Postlarvae were fed with a 1: 1 mixture of Isochrysis zhanjiangensis and Pavlova viridis over the course of experiment. Results showed that RDR was affected significantly by the first- and second-order effects of and first-order interactions among three factors, but the interactions were negative to the growth of pearl oyster postlarvae. Within the ranges of three factors examined, algal concentration was most important, followed by temperature in influencing the growth of P. fucata postlarvae. RDR was highly positively correlated with specific growth rate (SGR) and absolute growth rate (AGR). Simple linear regression equations of shell height-based growth rates regarding RDR were established, SGR (% d―1) = ―0.05 + 2.01RDR (R2 = 0.98); AGR (μm d―1) = ―0.02 + 2.82RDR (R2 = 0.96). Lack-of-fit test indicated their high adequacy. The models have greater advantages over conventional means of assessing somatic growth, and can be utilized to reliably evaluate recent growth of P. fucata postlarvae under concurrent variations of three factors examined in the present study.