THE GONADOTROPIN RELEASING HORMONE AGONIST, DESLORELIN ACETATE, IS CONTRAINDICATED FOR MITIGATION OF AGGRESSION AND REPRODUCTIVE BEHAVIOR IN MALE COWNOSE RAYS (RHINOPTERA BONASUS).

Abstract

Male cownose rays (Rhinoptera bonasus) can display aggressive behaviors toward other conspecifics. This can lead to accidental, self-inflicted trauma to the subordinate ray attempting to flee, such as rostral or ocular abrasions and ulcerations. Gonadotropin releasing hormone (GnRH) agonists, such as deslorelin acetate (Suprelorin^®), are commonly used among mammals for both reproductive management and behavioral mitigation, such as aggression in males. However, limited work has been done to advance our understanding of GnRH agonists in elasmobranchs. In an attempt to mitigate aggression, the use of deslorelin was investigated in three adult male cownose rays, that were implanted with either one (two rays) or two (one ray) 9.4 mg deslorelin implants. Another male ray was not implanted and used as the "control" male. Blood was collected from each ray prior to implantation, and then at various timepoints over 24 months, to evaluate plasma testosterone concentrations. Plasma testosterone was measured via enzyme immunoassay which was validated for this species. Behavior was monitored daily. The three males that received implants all had higher testosterone concentrations than the control animal two weeks to 24 months post-implantation. The ray that received two 9.4 mg implants displayed dose-dependent 50 to 100% higher concentrations compared to the two rays that received only one 9.4 mg implant. Testosterone concentrations in the control male were similar to previous published results. Implanted rays displayed increased aggressive and reproductive behaviors, that were not suppressed throughout the study. Female rays continued to be chased throughout the year, with some sustaining self-inflicted rostral abrasions requiring medical management. The deslorelin implants produced a persistent stimulation of testosterone production with no sign of suppression after two years. Based on the continued and sometimes enhanced unwanted aggressive behaviors, and failure of testosterone suppression, deslorelin is not recommended in male cownose rays for aggression and reproductive behavior mitigation.