The Japanese scallop(Mizuhopecten yessoensis),naturally occurring in Russia,Japan and North Korea,was introduced to China in 1980s.It is economically important and has become a major aquaculture species in the northern Yellow Sea.Recently,"Summer mortality syndrome" becomes a serious problem for scallop growers.During warm summer months,episodes of high mortality coincide with periods of elevated water temperature,low dissolved oxygen and disease outbreak.Mortalities appear to result from a poorly-understood interaction between high temperature,high density aquaculture,genetic depression and opportunistic infection by microorganisms.Resistance to summer mortality may be heritable in scallops,and phenotypic selection has been used to produce resistant strains in other bivalves.However,the broodstock of M.yessoensis used remains unselected in China.We initiated a family selection program for summer mortality resistance in 2011.Selective breeding programs for improving the scallop stocks are expensive,labor-intensive,and typically rely on lengthy field trials in which selection for survival is compromised by inherent stochasticity of outbreaks of "summer mortality syndrome".Reliable laboratory assays that identify and eliminate poor-performing families prior to planting could improve selection efficiency.We tested the hypotheses that juvenile survival after heat shock predicts adult survival at harvest for full-sib families of M.yessoensis.We heat-shocked(18 and 23 ℃)juveniles from each of 10 families,and monitored their survival for 5-20 days,then classified A08 and A09 families as high-surviving and the others as low-surviving.We also deployed replicated groups of siblings from all 10 families in coastal waters of Dachangshan Island,Dalian for one year.At harvest,we estimated family-specific average survival(%)and average individual shell height.We found that the high survival rates in both A08(34.3%±3.5%)and A09(46.5%±5.3%)families were identical with the predicted values after heat shock,and there was no family-level correlation between juvenile survival and shell height.We conclude that assays measuring heat tolerance in early juveniles hold promise of predicting performance of M.yessoensis families planted in coastal waters.