Abstract Experiments in the same flume and at the same ambient seston concentration showed that there was no significant difference in growth rates between juvenile and adult giant scallops Placopecten magellanicus Gmelin in the optimum velocity — ≈ 10 cm· s −1 — beyond which feeding/growth became inhibited. Our results appear to contradict those presented by Eckman et al. (1989) for bay scallops. We point out though that their comparisons between adult and juvenile scallops involved growth experiments at different locations and in different seasons and years. Hence, differences in seston quality and concentration were likely. Recent experimental evidence presented by Wildish et al. (1991) has confirmed that seston concentration interacting with flow is a determinant of scallop feeding inhibition, and so may provide an explanation for the contradictory results. Scallops forced to orient with their exhalant facing a unidirectional current at inhibiting flows grow more slowly than controls optimally positioned with respect to flow.