Statistical analysis

The data were tested for assumptions of normality (Shapiro-Wilk test) and homogeneity of variance (Levene’s test). To stabilize the variance, the data of female body weight and total body weight at 4–7 years of age were log-transformed. Differences between the sexes in TD and BW at 4–7 years of age, GI, number of acini at each gonad developmental stage, number of each gonad developmental stage in 10 acini per urchin, and gonad color (L*, a*, b*) were analyzed by the t-test. Skew of sex ratio was analyzed using the chi-square test. Significant differences in TD and BW among 4–7 years of age and GI by sex among August 2014, July, August and September 2017 were analyzed by one-way ANOVA, followed by the Tukey multiple comparison test. Percentage area of gametes, NPs and oocytes, spermatocytes, NPs, and unoccupied lumen at each gonad developmental stage were analyzed by Kruskal-Wallis test followed by Steel-Dwass multiple comparison test after arcsine transformation of these data. Correlations between TD and BW and between gonad color (L*, a*, b*) and GI, gonad development, and age were estimated using Spearman’s rank correlation. Statistical analysis was done using SPSS 19.0 and JMP 10 statistical software.