The basket cockle, Clinocardium nuttallii, is a candidate species for aquaculture in British Columbia, Canada. Previous research on broodstock conditioning, embryonic development and larval rearing of C. nuttallii demonstrated the potential for reliable hatchery production of cockle seed. In this paper, we investigated the e¡ects of culture density (50% and 150% bottom cover in a monolayer) and substratum (none and ¢ne sand) on cockle seed survival, growth, behaviour and shell morphology to improve the e⁄ciency of the nursery production phase. Low stocking density (50% cover) yielded a shell length increase from 3 to 7 mm over a 4-week period. High stocking density (150% cover) negatively impacted some of the growth and condition parameters studied, but did not have a statistically sig-ni¢cant e¡ect on seed survival. Growing seed without substratum did not signi¢cantly a¡ect seed survival or growth, but led to shell deformities (at shell length 415 mm) and lower burrowing rates when cockles were subsequently placed on sand. We recommend planting seed for grow-out at a shell length not exceeding 15 mm. Acclimating seed to the substratum before planting may increase the burrowing rates, thereby reducing the risks of seed dislocation and mortality. Additional studies are required to determine optimal substratum acclimation times and techniques.