Gentamycin controls bacterial growth during refrigerated storage of Piracanjuba, Brycon orbignyanus, semen

Abstract

Piracanjuba, Brycon orbignyanus, is an endangered Brazilian freshwater fish species. Refrigerated storage of semen is a simple and useful tool for artificial reproduction, especially when the number of brood fish is reduced. In our previous study, some extenders containing gentamycin were tested during refrigerated storage of piracanjuba semen. It was observed that semen stored in extender containing gentamycin did not retain sperm motility for longer periods compared to samples diluted in extender only, as expected. We hypothesized that the bacterial population present in piracanjuba semen was not susceptible to gentamycin, the gentamycin concentration tested did not control bacterial growth, or extender pH was not optimum for sperm storage. To test these hypothesis we (a) stored semen in NaCl-tris solution with the pH adjusted to different values; (b) quantified bacterial growth during the refrigerated storage of semen; (c) submitted some colony-forming units of different strains to susceptibility profile to penicillin, streptomycin, lincomicin, ampicillin, and gentamycin; and (d) evaluated the effects of gentamycin (0, 0.01, 0.1, 0.5, and 1.0 mg/mL) on bacterial growth, sperm motility and fertilization rate. Higher sperm motilities were yielded when extender pH was adjusted to 7.6. A progressive increase in bacterial population and a gradual reduction in sperm motility were observed during the 8 d of storage. Ninety-two percent of the bacterial colonies tested were susceptible to gentamycin. Semen diluted in NaCl-tris containing gentamycin at 0.1 mg/mL yielded higher motility and fully inhibited bacterial growth during refrigerated storage, and did not affect the fertilization process. Thus, the addition of gentamycin at 0.1 mg/mL of NaCl-tris pH 7.6 can be used as a routine when storage of semen for 4–6 d is necessary. The refrigerated storage of semen improves the efficiency of artificial reproduction and consequently can promote a better recovery of this species.