Brown trout Salmo trutta express different morphometrics due to divergence in the rearing environment.

Variation in the body morphology of juvenile brown trout Salmo trutta was studied for both wild and hatchery-reared individuals from the same gene pool. The thin-plate spline (TPS) method by pointing landmarks was used to characterize juveniles from their natal environment, the River Kuusinkijoki in eastern Finland, and from wild parents raised in a hatchery environment. Differences were found in the morphometrics of juvenile S. trutta from the two different environments. Wild S. trutta are characterized by a longer head and shorter anterior part of the trunk compared to hatchery S. trutta. Stocked to their natal river with wild S. trutta, the hatchery fish became characterized with more similar morphometrics to their wild counterparts. The characteristics of the body form are explained by the differing environmental conditions in the wild and hatchery. It is concluded that a simple hatchery environment may delay the development of morphological characteristics important in a natural river environment.