Unbalanced parental contribution and small effective population size(N e)are common issues during the artifi cial breeding of marine bivalves.The impact of hatchery-spawning practices on parental contribution,effective population size,the N e/N ratio,and genetic diversity are largely unknown.To address this,we conducted a parentage analysis on a complete 3×3 diallel cross of clam M eretrix meretrix using eight microsatellite markers.The genetic diversity of the parents was higher than that of their respective offspring in most crosses(8/9).Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross,and the same parent clam exhibited large variation in parental contribution among different crosses.The variance in male contribution was higher than that of the female contribution in most crosses,suggesting that male contribution was more skewed than for females.The N e/N ratio for nine crosses ranged from 0.58 to 0.86.There was no linear relationship between the sex ratio and the N e/N ratio(P>0.05).Moreover,a sex ratio closer to one-to-one does not necessarily mean a larger effective population size.A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio. Unbalanced parental contribution and small effective population size (Ne) are common issues during the artifi cial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effective population size, the N e / N ratio, and genetic diversity are large unknown.To address this, we conducted a parentage analysis on a complete 3 × 3 diallel cross of clam M eretrix meretrix using eight microsatellite markers. the genetic diversity of the parents was higher than that of their respective offspring in most crosses (8 / 9) .Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross, and the same parent clam show large variation in parental contribution among different crosses. The variance in male contribution was higher than that of the female contribution in most crosses, suggesting that male contribution was more skewed than for females. The N e / N ratio for nine crosses ranged from 0.58 to 0.86. There was no linear rela tionship between the sex ratio and the Ne / N ratio (P> 0.05) .Moreover, a sex ratio closer to one-to-one does not necessarily mean a larger effective population size. A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio.