Abstract
The synthetic steroid 17α-methyltestosterone (MT) is used as a feed additive to produce predominately male populations of tilapia ( Oreochromis sp.). The legal use of MT by the U.S. tilapia industry requires an approved New Animal Drug Application (NADA) from the U.S. Food and Drug Administration (FDA). The present study was conducted to satisfy the remaining FDA data requirements in the area of product chemistry. The results indicated that (1) MT-treated feed is homogenously mixed during the manufacturing and bagging process, (2) MT remains uniformly distributed throughout the feed during prolonged storage at room temperature, and (3) MT concentrations in fish feed are stable for at least several months when feed is stored at 4 °C or lower, but decline linearly with time at higher temperatures. The half-life of MT (i.e., the time required for the MT concentration to fall from 60 mg/kg to 30 mg/kg) was 1.1 and 4.8 months for feed stored at 40 °C and 22 °C, respectively.
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