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Growth rates, as estimated by the RNA:DNA ratio, were determined for planktonic postlarvae and for recaptured and wild newly settled benthic stages (fifth and sixth instars) of the American lobster Homarus americanus. The mean growth rate of planktonic postlarvae in 1994 was 0.522 ± 0.247 mg protein d-1. This was significantly higher than planktonic growth rates observed in 1991 (0.449 ± 0.121 mg protein d-1) but not in 1992 (0.460 ± 0.144 mg protein d-1). The percentage of poorly nourished planktonic postlarvae, those with growth rates <0.220 mg protein d-1, ranged from 3 to 13% in 1991, 1992 and 1994 and was similar to that observed in previous years (1988 to 1990). Newly settled lobsters had significantly lower mean growth rates (0.223 ± 0.180 mg protein d-1) than planktonic postlarvae. Recaptured lobsters originating from wild stock had significantly higher growth rates than those originating from laboratory stock (0.281 ± 0.176 vs 0.085 ± 0.078 mg protein d-1, respectively). Laboratory rearing effects (lowered growth rates) appeared to persist even after 1 wk in the field. The differences in the growth rates between planktonic and benthic phase lobsters may be evidence of a trade-off between slow growth due to decreased food ingestion and potential increased vulnerability to predation when actively foraging.