Effects of size grading on survival, metamorphosis, and growth of the Chinese pearl oyster, Pinctada martensii

Growth heterogeneity is a problem in shellfish culture production, which can affect growth, survival, and metamorphosis. In this study, we conducted an experiment to investigate the effects of size grading on survival, metamorphosis and growth of larvae and juvenile Pinctada martensii in Beihai, Guangxi Province, China. Three to 5-week-old larval or juvenile P. martensii were graded five times and sorted into a “small group” (S), “large group” (L), and “control group” (C) each time. In general, the survival rates in the S groups and L groups were influenced by size grading. S groups had higher survival rates than that of the C group in the first two gradings. The metamorphosis rates in the S groups were higher than that of the C group, indicating that size grading increased the metamorphosis rates of the S groups. Grading promoted a compensatory growth effect in the S groups. S groups generally had higher Specific Growth Rates than that of L groups and the average shell height of S groups exceeded L groups at the end of the experiment. Grading had little effect on the ratio of shell width and shell height in this experiment. Coupled with appropriate stocking densities, size grading could reduce intraspecific competition, improve growth rate and hatchery efficiency, and ultimately reduce culture costs. •High potential to improve growth rates through size grading in Pinctada martensii.•A breeding practices for P. martensii can be designed based on these results.•Survival and metamorphosis rates of small size had been improved during the progress of size grading.•The time of nuclear implantation may be advanced during the process of increasing the growth rate.