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Sea urchins were stocked at a density of 15(D15),30(D30),45(D45)and 60(D60)urchin/cage(0.2×0.3×0.4 m3)in a laboratory culture environment for 16 months.The body weight(BW)growth was monitored at an interval of two months during the whole experimental period.At the conclusion of the experiment,the survival sea urchins were counted and the gonad wet weight(GW)and gonad colour were measured.Special growth rate(SGR)of body weight,survival rate(SR),gonad index(GI),gonad colour difference(ΔE00),coefficients of variation of BW,GWW,GI and ΔE00,yield of BW and yield of GWW per cage were calculated.Over the experimental period,mean weight of the sea urchin under different stocking densities decreased as the density increased.Density significantly affected final BW,SGR,GWW and GI(P<0.01),with the density D(15)had the best performance and the D(60)performed the worst in all the four variables.However,density had no significantly effect on SR.There was a significant effect of density on gonad colour(ΔE00)(P<0.05)with the D(15)the best.Coefficient of variation of BW decreased as the sea urchin grew.Sea urchins held at low densities achieved a more uniform BW,GWW and GI than those held at high densities.An increase in total yield of BW so as GWW with increased density was observed and could be described by the following equations: Yield of BW(g)= 16.8 □ R2=(0.850),Yield of GWW(g)= 1.1□ density + 58.3(R2=0.363).However,when the sea urchins of which the GI over 10%or 12.5%were selected,there were no significant differences among the four density treatments in the yield of BW and GWW.