Researchers compared two European eel sperm freezing methods from Spain and Hungary to find the best way for captivity breeding. They tested sperm quality after thawing using a computer system and flow cytometry to check viability. They also looked at DNA changes caused by the freezing process. Results showed the methanol-based method had better sperm motility, velocity, and live sperm percentage. Sperm DNA methylation levels were lower in the DMSO method. Overall, the methanol method preserves European eel sperm better for future breeding efforts.