Semen collection methods affect the bacterial composition of post-thawed semen of silver barb (Barbodes gonionotus)

Biosafety issue associated with the risk of pathogenic contamination of cryopreserved semen is a common concern because of associated declines in sperm quality, storage period and disease transmission. This study was conducted to evaluate the effects of methods of semen collection on sperm quality and bacterial composition of post-thawed semen of silver barb (Barbodes gonionotus). Semen collection methods consisted of four treatments: (1) hand-stripping of abdomen without rinsing of urogenital area with water, (2) hand-stripping of abdomen after rinsing of urogenital area with water, (3) catheterization without rinsing of urogenital area with water and (4) catheterization after rinsing of urogenital area with water. Semen diluted with calcium-free Hank's balanced salt solution containing 10% dimethylsulfoxide (DMSO) was frozen at a freezing rate of -8°Cmin(-1) before plunging in liquid nitrogen. Post-thawed semen collected by catheterization after rinsing urogenital area had the lowest bacterial number, about 2-log reduction of total heterotrophic, Gram negative and pseudomonad bacteria, compared with the other three collection treatments. However, percentages of motile and viable sperm were not significantly (P>0.05) different among treatments. This method eliminated Flavobacterium aquatile, Bacillus megaterium, Kocuria varians, Staphylococcus haemolyticus and Aeromonas media in cryopreserved semen. This is the first report demonstrating the effects of semen collection methods on bacteriological quality of frozen-thawed fish semen.