Evidence for reduced genetic variation in severely deformed juvenile salmonids

Inbreeding is one of the factors that can result in high infant mortality. In many species, however, mortality at early life stages is very difficult to observe in the wild and estimates from later life stages may therefore underestimate the effects of reduced genetic variability on fitness. Using microsatellites, we compared the amount of genetic variation in severely deformed fry of Lake Saimaa salmon (Atlantic salmon, Salmo salar) and brown trout (Salmo trutta) hatchery brood stocks with normal fry from the same brood stocks. We observed significantly lower standardized heterozygosity and higher internal relatedness values for deformed fry of both species compared with normal fry. Our results suggest that (i) inbreeding can be an important factor causing severe deformities in juvenile salmonids and (ii) high mortality of severely deformed low heterozygosity individuals in early life stages may partly explain why some studies exploring heterozygosity–fitness correlations fail to find any association. An important direction for future research on this topic will be to compare the results of experiments conducted in captivity with those of similar experiments conducted in wild or semi-wild conditions, as such studies would help to better understand the direct relevance of research conducted in captivity with respect to the conservation of wild populations.