Production results for flow-through larval cultures in a hatchery showed that there were no correlation between yield of pediveligers and initial stocking density when 36 larval batches were stocked between 2.9 and 12.6 larvae mL−1 (Magnesen et al., 2006). In flow-through cultures at 17 cells L−1 the yield of pediveligers collected on 150 m mesh decreased when initial stocking density increased above 4 larvae mL−1, and the total number of pediveligers
decreased when it exceeded 8 larvae mL−1 (Andersen et al., 2007).However, algal feed concentration in the hatchery cultures varied between 8.2 and 17.8 cells L−1, and season significantly affected the results as the best results were obtained close to the production season in the wild (Magnesen et al., 2006). This is consistent with the work reported by Robert and Gérard (1999) when both larval growth rate and yield of pediveligers were affected by season with best results in April–May. They explained the seasonal difference in growth rate and yield with variations in initial egg quality. Our first experiment (June) was performed close to the natural spawning time (July/August), while the second was in mid-winter (February).Number of larvae from eggs was much higher in June (54%) compared to winter (32%) and could indicate better egg quality, but larval yield was similar (40% ready to set of initial numbers). The yield from RAS tanks was, however, much lower (16.4%)