Tricaine methanesulfonate and eugenol during semen collection do not affect fertilization and hatching rates on Rhamdia quelen.

The reproduction of some fish species in captivity is only possible by imposing artificial reproductive procedures, and the manipulation of fish for these purposes is a stressor. Thus, anesthesia can reduce stress during handling. However, it is necessary to investigate the possible side effects on breeding and the general health of the animal. Therefore, we aimed to investigate the impact of tricaine methanesulfonate (MS-222) and eugenol (EUG) at concentrations of 300 mg L-1 and 40 mg L-1, respectively, on several stress- and reproductive-related parameters in Rhamdia quelen anesthetized before semen collection. After hormonal induction, 24 sexually mature males (534.4 ± 259 g) were randomly assigned to treatment groups and semen and blood samples were collected. Anesthesia recovery and induction time were extended in fish anesthetized with EUG; however, plasma cortisol concentrations did not differ among the treatment groups. EUG caused higher DNA fragmentation in blood cells than in the control group (without anesthesia). EUG increased the monocyte count compared to the other experimental groups. MS-222 showed a lower sulfhydryl group (SH) quantitation than the other experimental groups. The anesthetics used before semen collection in this study had no adverse effects on the fertilization or hatching capacity of anesthetized R. quelen. MS-222 (300 mg L-1) and EUG (40 mg L-1), despite being related to hematological and semen changes, did not negatively affect the reproductive capacity of R. quelen males. Thus, anesthesia is recommended for R. quelen during semen collection, considering reproductive parameters and animal welfare.