Methyltestosterone in Field Efficacy Trials Prepared by:

Various techniques have been developed for the control of sexual differentiation in a variety of fish species, including the use of the androgen, 17-alpha Methyltestosterone (MET). Specifically, this compound has been used effectively in the U. S. under compassionate INAD Exemption #11-236 on early life stage tilapia to produce predominately male populations (i.e., sex reversal). In calendar year 2006 (CY06) the efficacy of MET was evaluated in 240 trials involving approximately 24.2 million early life stage tilapia for sex reversal. Trials were conducted at 1 USGS Co-op Unit, and 11 commercial tilapia culture facilities. The compassionate study protocol under which treatments were administered allowed the investigator to administer MET at a dosage of 9 mg MET/kg of fish biomass for 28 consecutive days (60 mg MET/kg feed when fed at a rate of 15 % body weight). Overall, results from trials conducted in CY06 indicated that treatment appeared either effective (in approximately 72 % of the trials) or were characterized as inconclusive (in the remaining 28 % of the trials). Based 2on results from CY06, it appears that MET is an effective compound for sexual reversal of early life stage tilapia