Sperm DNA fragmentation in zebrafish (Danio rerio) and its impact on fertility and embryo viability — Implications for fisheries and aquaculture

• Significant differences found for sperm DNA fragmentation in zebrafish
• Correlation existed between embryo viability and baseline sperm DNA fragmentation.
• Zebrafish with greater sperm DNA longevity yielded better embryo viability results.

Sperm DNA damage is one of the many factors that have been associated with male infertility. However, sperm DNA fragmentation (SDF) assessment has been challenging because protamines render the nuclear chromatin highly compacted. For those fish species having sperm with protamines, one hypothesis is that the less compacted DNA could be more vulnerable to iatrogenic damage when used in artificial reproduction. The present investigation included three objectives: 1) apply the Sperm Chromatin Dispersion (SCD) technique using the Halomax-SCD test kit (Halotech DNA, Madrid, Spain) for the rapid assessment of SDF in zebrafish (Danio rerio); 2) assess the dynamic aspects of SCD to determine zebrafish sperm DNA longevity in both activated and unactivated samples; and 3) to analyze if the dynamic level of zebrafish sperm DNA fragmentation has any impact on fertility and embryo viability. The results demonstrate the use of the Halomax-SCD test for assessing SDF in zebrafish and are congruent with results of DNA Breakage Detection-Fluorescence In Situ Hybridization (DBD-FISH) and Comet Assay. The averaged SDF values derived from 10 individuals were low immediately after sperm motility activation (1.4% ± 0.96) compared to 15 min later (10.6% ± 9.96), with increasing and very high rates of SDF (r-SDF), 0.6% units/min. Although SDF did not significantly influence oocyte fertilization capacity, it significantly impacted later embryo development and overall reproductive success, i.e., fertility rates higher than embryo viability values.