Fate of Methyltestosterone in the Pond Environment: Use of Mt in Earthen Pondswith No Record of Hormone Usage

The following study examined the persistence of 17α-methyltestosterone (MT) in the environment after its use for masculinizing Nile tilapia in nursery ponds located in the Universidad Juárez Autónoma de Tabasco, Mexico. Fry harvested from spawning ponds were treated with a masculinizing dose of MT (60 mg kg-1) for four weeks. Concentrations of MT were determined by radioimmunoassay. MT was not detectable in the water at any time. In the sediments, MT was not detectable during the first 10 days of treatment. Afterwards MT was detectable in all sampling points (mean = 146.7 pg g-1; SE = 21.3). MT values varied from not detectable to 368.9 pg g-1. Masculinizing efficiency was low in the first trial (87.4% males) but increased significantly afterwards, reaching 92.6% males in the second trial and 98.7% in the third trial. Another outcome of this investigation is a manual on tilapia masculinization using synthetic steroids. This manual is intended to reach fry producers, extension agents and technicians; it contains a general description of the biology of the tilapias, traditional culture practices, masculinization methods, and a detailed section on safe handling of steroids. NINETEENTH ANNUAL TECHNICAL REPORT 104 to a grow-out pond and fed with regular fish food. At 90 to 100 dpf, sex ratios were determined by microscopic examination (10 and 40X) of gonads using squash preparations in Wright’s stain (Humason, 1972). The weights of sampled fish were recorded at this time. To collect water and soil samples, three sampling points were set along the pond as follows: points 1 and 3 were located under treatment hapas (1 = control treatment; 3 = MT treatment); the other sampling point was located in the middle of the pond. Water samples (12 ml) were collected with pipettes into 15-ml polypropylene tubes and stored at –20°C until analysis for MT. Soil core samples were collected with long 1.25-cm-diameter PVC pipes, placed in Whirl-Pak bags, excess water poured off, and stored at –20°C until shipment to Oregon State University (OSU) for analysis. All water and soil samples were collected early in the mornings, before initiation of feeding. Samples were taken weekly starting five days before the onset of the experiment (23 February).