Spawning season movements of transported landlocked Atlantic salmon in a newly restored river habitat

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Foraging, swimming performance and morphology of semi-wild and hatchery-reared landlocked salmon juveniles

The Saimaa landlocked salmon (Salmo salar m. sebago) in Finland is a critically endangered ecomorph due to the historical damming of rivers. The morph has been dependent on stockings of hatchery-reared juveniles for more than 40 years. Recently, various efforts have been taken to restore some of the earlier reproduction areas to return the natural life cycle. However, as the population has been reared in hatcheries over many generations and as the released fish generally suffer high post-release mortality, it is crucial to know whether domestication has affected the population’s fitness-related traits and to assess how the developmental environment affects salmon’s phenotype. In the present experiment, we studied the role of the early developmental environment in trait formation by comparing juveniles (0+ years) from three different backgrounds: 1) semi-wild fish from the River Ala-Koitajoki (stocked as alevins), 2) fish grown in standard hatchery rearing conditions and 3) fish grown in enriched hatchery rearing conditions. All the study fish originated from the same generation and had the same genetic background. We tested their capability of feeding on natural prey, critical swimming speed and studied their morphology. Our preliminary analyses indicate notable background-dependent variation in all the studied traits. Semi-wild fish consumed more natural prey items, had higher critical swimming speed and differed in their fin morphology, when compared to hatchery reared fish. The developmental environment seems to produce differences in key traits, but how this is linked to survival in the wild remains to be studied in the near future.peerReviewe

Early winter foraging success, swimming performance and morphology of juvenile landlocked Atlantic salmon reared under semi-wild and hatchery conditions

Several Finnish populations of salmonids have been maintained exclusively by stocking hatchery-reared fish for several generations, and it is crucial to know whether domestication has affected fitness-related traits and to assess how the developmental environment influences fish phenotypes. Here, we focused on Lake Saimaa landlocked salmon (Salmo salar m. sebago) and studied the role of the early rearing environment in trait formation by comparing juveniles (fingerlings) from three backgrounds: (i) semi-wild (stocked as alevins), (ii) standard hatchery, and (iii) enriched hatchery conditions We compared juvenile morphology, swimming performance, and capability of feeding on natural prey in early winter. We found no differences between standard and enriched hatchery conditions. Semi-wild fish consumed more prey items, but wet mass of stomach contents did not differ among backgrounds. Swimming endurance was comparable among backgrounds. Semi-wild fish had slenderer body shape and longer fins than hatchery-reared fish. The lack of performance differences between hatchery juveniles and their semi-wild conspecifics is possibly due to reduced phenotypic plasticity caused by extremely low levels of genetic diversity in this population.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author