As one of the most popular species for fly-fishing, Adriatic grayling (Thymallus aeliani) is under constant fishing pressure. Natural populations are thus being stocked, as recuperation, with graylings raised and bred in fish farms. Environment in fish farms is greatly altered compared to natural habitat resulting in drastically different selective pressure acting on these fish compared to their wild conspecifics. Although most of hatchery reared individuals do not survive when released into the wild, some nevertheless interbreed with wild grayling, reducing the overall fitness of population and its ability to adapt to changes in natural environment. The Soča river has been stocked with hatchery reared grayling for decades. In an effort to reduce accumulative selection in captivity, the progeny propagation relies on male breeders caught in the wild, coupled with hatchery based female breeders. To investigate selection pressure in hatchery environment we deep sequenced 12 hatchery reared individuals at age 1+, and 12 wild individuals caught in the Soča river. Genomic scan was performed with double-digest restriction site associated DNA sequencing (ddRADseq) using PE-125bp chemistry. Obtained SNPs were classified as neutral or potentially adaptive, with the former used for calculating population statistics, and the latter to identify potential selection in hatchery environment. Selection signature in genes with immune function (MHC genes, immunoglobulin gene) was detected, suggesting compromised immune response of hatchery reared individuals when compared to their wild counterparts when in natural habitat, reducing hybridized populations ability to resist naturally present pathogens. Directional selection in hatchery environment was also observed at growth hormone gene, potentially favoring fast growing individuals that thrive when surplus food is present, a situation rarely observed in the wild. These preliminary results suggest a reduction of fitness for hatchery reared individuals when introduced into the natural habitat, envisaging the need for emendation of current Adriatic grayling management plans, to support a sustainable fisheries management in the near future. Sequencing of additional grayling populations is on the way, to clarify this question more thoroughly.
B.06 Other
COBISS.SI-ID: 4163720ddRAD seq analysis showed that of the 42,000 loci diagnostic for Adriatic grayling, only ca. 9% of those that separate genetically pure museum specimens of Adriatic grayling from the Soča River and Adriatic grayling from the Sesija River, which indicates a high genomic similarity of these two groups. In our opinion, therefore, the rescue of the marble grayling could be successful mainly by transferring specimens from the Session. The high FST value (0.33) observed between marble museum and session samples at polymorphic loci (8k / 118k) could have a certain impact on the success of colonisation of transferred fish during transfer due to environmental change, so stabilisation conditions should be provided. and adaptation of the newly settled population, eg a multi-year ban on sport fishing as well as any other disruptive interventions in the water.
F.27 Contribution to preserving/protecting natural and cultural heritage
COBISS.SI-ID: 4209288