| 17α-methyltestosterone (MT), a synthetic androgen drugs, has served as a specific medicine on fry culture and gender control in aquaculture. It was found that there were MT residues in tilapia at the market, which would harm the human body as this androgen has great potential hazard on human health. Studies were conducted on the dissipation of MT in Nile tilapia Oreochromis niloticus (L.) fry that received dietary of MT to induce sex reversal and adult Nile tilapia Oreochromis niloticus (L.) that received dietary of MT to promote the growth under aquaculture model, aimed for providing theoretical support for security control of fishery drugs in aquaculture and monitoring of drug residues in tilapia tracing, which was based on the optimized high-performance liquid chromatography method for determination of MT residues in tilapia tissues and tilapia fry.First, by comparing the domestic and foreign studies, a simple high-performance liquid chromatography method for determination of MT residues in tilapia tissues and tilapia fry have been optimized. Samples extracted by ether ultrasonic extraction, purified by petroleum ether (plasma, bile supplemented by SPE extraction), separated by using a ODS-C18 analytical column with methanol water (the ratio was 77%) and UV detector, determined by the external standard method, which had a suitable retention time, good peak shape, target peak and impurity peaks can completely separated, the method got good linear relationship in the range of 0.040μg/mL~10.0μg/mL MT concentration (R2 = 1.0000). The limit of detection for samples were: 8μg/kg for dorsal muscle and abdominal muscle, 27μg/kg for fishskin and liver, 80μg/kg for gonad, 80μg/L for plasma, bile, 20μg/kg for fish fry. The recoveries obtained from these samples were above 80.6%, with the relative standard deviation were below 5.53%. This method was appropriate for MT determination, at the same time laid a foundation for doing the research on the dissipation law of methyl -testosterone residues in tilapia.Based on the method of determination MT residues in fry, studies were conducted on the dissipation of MT in Nile tilapia Oreochromis niloticus (L.) fry that received dietary of MT to induce sex reversal under aquaculture model. Sexually undifferentiated Nile tilapia fry (8mm~10mm, 9mg~13mg) were fed on a diet containing unlabeled MT (200mg/kg, 50mg/kg, 20mg/kg) for 30d to effect masculinization in the concrete tank, daily feeding was regularly, water was changed once a week, shed was used natural to control the temperature. After 30d, the fry were transferred to a pond with normal feed, MT in fry were dissipation in the natural environment. The fry were sampled in different time and frequency in the latter days, then MT residues in fry were measured by high performance liquid chromatography (HPLC), SPSS Statistics 17.0 combines EXCEL 2003 statistical software were applied to the data processing and analysis in order to get the dissipation rule of MT after tilapia sex reversal. The results showed that MT residues in tilapia fry almost maintained consistently during the sex reversal period, although overall trend of the dissipation was still downward while multi-peak phenomenon occurred in the dissipation of MT between two feedings. Besides, though masculinization rate of MT was ideal, following the withdrawal, the dissipation of MT fitted with exponential decline and the dissipation was slowly in the latter. the higher the concentration of MT that fed to tilapia for sex reversal, the longer time MT residues maintained in tilapia fry.If the farmers use excessive MT for sex reversal of tilapia privately, there would be some MT residues in marketing tilapia that can't eliminated completely before marketing, then it will take some harm to consumers. Strongly recommends that national authorities develope alternative methord for masculinization as soon as possible, which will fundamentally protect the interests of farmers, while eliminate MT use.Recently, MT determination of tilapia often turns up positive results. Studies were conducted on the dissipation of MT in adult Nile tilapia Oreochromis niloticus (L.) that received dietary of MT to promote fish growth under aquaculture model, tilapia weighed approximately 250g were fed on a diet containing unlabeled MT (200mg/kg) for 3d for promote fish growth in the concrete tank, After 3d, the tilapia were transferred to a pond with normal feed, MT in tilapia were dissipation in the natural environment. The tilapia were sampled in the latter days, then MT residues in tilapia tissues were measured by high performance liquid chromatography previously established,DAS 2.1.1 drug metabolism analysis software combines EXCEL 2003 statistical software were applied to the data processing and analysis in order to get the dissipation rule of MT in tilapia tissues. The results showed that the dissipation of MT in dorsal muscle, abdominal muscle, fishskin, bile, plasma, liver, gonad all fitted with exponential decline, of which the dissipation of MT in plasma fitted with index decrease. MT were distributed in various tissues, tissue-MT concentration was down in the order: bile, liver, gonads, plasma, skin, abdominal muscle, dorsal muscle, which suggested that metabolism of MT in fish was hepatobiliary metabolism. Under these conditions, MT residues in tissue is no longer detected following withdrawal 1164h in 49d, in which MT residues in plasma was no longer detected following withdrawal 804h in 34d. Suggested that drug metabolism was slowly, using MT promote fish growth in adults stage, there would be some MT residues in marketing tilapia that can't eliminated completely before marketing. For consumer safety, MT use must be forbidden in adult fish stage, relevant departments should severely punish farmers that using MT in adults stage privately, also should enhance feed formula optimization for growth of tilapia purpose, so that farmers are willing to completely abandon the use of MT.
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