Rheotactic response-the directional response to water current-was compared between two strains of juvenile landlocked Atlantic salmon Salmo salar to determine the presence of inherited migratory differences. Juvenile rheotactic response was examined because it is known to be an inherited behavior in other salmonids. An inlet-spawning strain (Sebago Lake, Maine) and an outlet-spawning strain (West Grand Lake, Maine) were compared in common experimental environments. The strains were compared as newly hatched fry (age 0) and were expected to remain instream for a year. Fry movements were compared in indoor artificial stream channels in 1999 at two levels of water velocity (6 and 12 cm/s) and density (one fish/m(2) and two fish/m(2)). The inlet strain fry (Sebago Lake strain) had a stronger positive rheotactic response (upstream movement) than the outlet strain fry (West Grand Lake strain). Age, density, and water velocity also affected fry movement: upstream movement was lower in older fry, downstream movement was higher at high density, and the proportion of fry that moved (either upstream or downstream) was lower at high velocity. Salmon were also compared as smolts (age 1) when they were expected to migrate lakeward. The strains were compared in outdoor artificial stream channels in 1998 and 1999. Outlet strain smolts (West Grand Lake strain) had a stronger upstream response than inlet strain smolts (Sebago Lake strain), consistent with the expectations for lakeward-migrating smolts. The fry and smolt experiments indicated that inlet and outlet strains had different rheotactic responses that changed ontogenetically. These differences may be best explained by local adaptations to native habitat conditions. Because innate movement may affect the survival of juvenile salmon stocked for population restoration or provided to sport fisheries, strain and environmental conditions must be considered when stocking landlocked salmon into new habitats