Fig. 1. (A) The relationship between log₁₀ body mass and growth period in seawater for the treatment groups of PIT-tagged Atlantic salmon (Salmo salar) studied. Salmon were reared either under ambient photoperiod (cage 1, filled circles; cage 2, filled triangles) or were subjected to 24 h continuous lighting from 1 November 2000 to 18 June 2001 (cage 3, open circles; cage 4, open triangles). (B) The condition factor [(body mass/fork length^-3)x100] for the treatment groups of salmon during and shortly after photoperiod manipulation. The symbols and number of fish studied are as in A. The period of continuous lighting in cages 3 and 4 is illustrated by the grey box. Values represent means ± S.E.M. The number of fish sampled from each cage and treatment is shown in Table 1.