Comparative body shape variation of the European grayling Thymallus thymallus (Actinopterygii, Salmonidae) from wild populations and hatcheries

We employed geometric morphometric techniques to investigate external (body) morphology of European grayling (Thymallus thymallus) populations from the wild and hatchery facilities. Wild graylings were representative of Balkan and Caspian phylogenetic clades, whereas hatchery-reared specimens originated from Balkan and Adriatic phylogenetic clades. Individuals of T. thymallus from the Adriatic phylogenetic clade were the largest, followed by those from the Balkan phylogenetic clade, while graylings from the Caspian phylogenetic clade were the smallest. Graylings from hatchery facilities were larger than graylings from the wild. Body shape variation in T. thymallus coincides with genetic differentiation of the analyzed populations, whereas it is less influenced by difference in environment they experience in wild and captive habitats. Although hatcheries can generate large numbers of individuals, some of which will have an extreme phenotype, the variance in body shape was similar in captive and wild populations. Allometric relations were different between specimens from the wild and from hatchery facilities, as well as among those belonging to different phylogenetic clades. Allometric analyses performed separately for the wild and hatchery-reared populations revealed significant effect of allometry and similar trends in size-related shape variation among populations from different phylogenetic clades. We found that phenetic relationships among the studied wild grayling populations inferred from non-allometric body shape variation better reflected their phylogenetic relationships than equivalent data from hatchery populations.