A method is described in which a single bone, the first vertebra, is used to distinguish bone remains of juvenile salmon (Salmo salar) and trout (Salmo trutta) with 90% certainty. A single regression of salmon and trout first vertebra-width versus fish-length of fish predicted the latter with an accuracy of ±<10 mm (95% confidence limits) for salmonids of 45–150 mm fish-length. First vertebrae were assigned to salmon or trout based on three visual characters with 89%,–90% certainty. Salmon are more variable than trout for the three characters. Of first vertebrae, 6.5% were not readily identifiable as either salmon or trout, and a further 3.0%) were misclassified using our criteria.