In wild Atlantic salmon, Salmo salar, of Armorican rivers, precocious maturity occurred at <5% at age 0+ (males only). At 1+ (in both sexes) the percentage occurrence varied between years and stretches of river. Spawning marks on scales of smolts and anadromous adults confirmed that such fish smoltify after spawning. From back-calculation from scales of R. Scorff salmon it was found that: (1) mature parr were larger than immature fish at 1+ in autumn and at smolting; (2) mature 1+ parr had been intermediate in length between upper and lower modal group fish in their first autumn. It is suggested that in western France a holobiotic cycle for the Atlantic salmon can occur before the amphibiotic one as an adaptive strategy.