In a study on male freshwater stingrays, giving them a GnRH vaccine or deslorelin (a GnRH‑like peptide) implants didn’t stop them from making sperm or behaving aggressively. The vaccine did nothing to testosterone levels, while the implants actually pushed testosterone way up for over a year, which could be harmful. So, at the doses used, these methods didn’t work as a chemical birth‑control and might even cause unwanted hormone spikes.

Very little information is available in veterinary literature concerning chemical contraception in elasmobranchs. To decrease breeding and adverse reproductive behaviors, male <i>Potamotrygon</i> sp., housed in two zoologic institutions, were treated using methods used in other elasmobranchs. Four animals received deslorelin acetate implants (Suprelorin 4.7 mg and 9.4 mg), four animals received a gonadotropin-releasing hormone vaccine (Improvac 50-100 &#xb5;g) twice separated by 1 mon, and two animals were not treated to serve as controls. Health checks, including blood sampling, coelomic ultrasound, and sperm analysis, were performed bimonthly and then monthly over almost 2 yr. Microscopic examination of sperm never revealed any significant change in concentration or motility. Size of testes and seminal vesicles glands did not change significantly after treatment. Plasma testosterone concentrations were stable (&#x223c;1 ng/ml) in intact and vaccinated animals throughout the study period. Plasma testosterone level increased significantly after deslorelin implantation and remained very high for at least 13 mon, never returning to initial values. Peak concentration varied according to the deslorelin acetate concentration used. Aggression toward females continued despite the use of contraception. Histopathologic examination on dead stingrays revealed active testicular tissue. These results suggest that deslorelin acetate implants and GnRH vaccine are ineffective at dosages used in our cases. Implants caused a continuous stimulation of the hypothalamic-pituitary-gonadal axis that could be harmful for the animals.