Exploring the occurrence of DNA-fragmentation in Arctic charr sperm (Salvelinus alpinus) and its impact on embryo viability

Sperm from Arctic charr sires can contain high levels of DNA fragmentation. Nevertheless, the frequency of this phenomenon and its impact on embryo viability are not fully known. The current study aimed to further elucidate the extent of DNA fragmentation in Arctic charr sperm through a comprehensive sampling of Swedish hatcheries. Furthermore, associations between sperm DNA fragmentation and subsequent embryo viability were investigated. Arctic charr males ( n = 166) were sampled from five major Swedish hatcheries, and DNA fragmentation, together with sperm concentration and viability, were recorded. Fragmentation levels were classified as: intact, moderate, severe, and stellar fragmentation. The median DNA fragmentation level (severe to stellar fragmentation) was 32 % (5–50 %; n = 93). Moreover, the median sperm concentration was 3.6 × 10 9 cells/ml (range 0.3–11.5 × 10 9 ) and cell viability was 90 % (range 68–96 %). Significant differences in sperm concentration, cell viability, and DNA fragmentation were found among the five hatcheries (Kruskal-Wallis, p < 0.05). The effect of sperm concentration on sperm cell viability was significant ( p < 0.001). A strong Spearman correlation coefficient ( ρ = 0.76, p < 0.05) was observed for severe or the sum of severe and stellar DNA fragmentation with early embryo mortality. In conclusion, DNA fragmentation levels were notably high in farmed Arctic charr while individual fragmentation levels were clearly associated with the timing of embryo abortions in the offspring. However, the impact of sperm DNA fragmentation on the overall embryo viability during routine hatchery production remains uncertain. • DNA fragmentation, concentration, and viability were recorded in Arctic charr milt. • High levels of sperm chromatin dispersion (SCD) were found at all involved hatcheries. • SCD showed a stronger correlation with the timing of embryo mortality than with overall survival.