Selection or adaptation: Differences in growth performance of juvenile turbot (Scophthalmus maximus Rafinesque) from two close-by localities off Norway

Growth performance was investigated in two populations of juvenile turbot ( Scophthalmus maximus Rafinesque) from two close-by localities on the Norweg ian coast, both caught at the southwest coast and called SW1 and SW2, reare d together under four different temperature regimes. All growth indices sho wed that the growth performance of the SW1 Norwegian population was superio r compared to the SW2 Norwegian population especially at the extreme temper atures. Our findings may indicate local adaptation of turbot. We discuss if local adaptation will be reflected in neutral genetic markers as the varia tion in growth is higher than the genetic variability previously reported f or this species, which might make the non-neutral markers a better tool to understand local adaptation of fish populations. Alternatively our results could indicate hatchery selection or a strong genetic drift which may cause a substantial genetic change eventually leading to inbreeding depression w hich again may cause decreased growth.