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Aquaculture CRSP 21st Annual Technical Report
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55
Studies on Fate of Methyltestosterone and its Metabolites in Tilapia and on the Use of
Phytochemicals as an Alternative Method to Produce a Monosex Population of Tilapia

Tenth Work Plan, Reproduction Control Research/Experiment (10RCR1)
Final Report

Konrad Dabrowski, Gustavo Rodriguez, Kyeong-Jun Lee, and Mary Ann G. Abiado
School of Natural Resources
The Ohio State University
Columbus, Ohio, USA

Wilfrido Contreras Sanchez and Gabriel Marquez-Couturier
Universidad Juarez Autonoma de Tabasco
Tabasco, Mexico

Ronald Phelps
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, Alabama, USA


Abstract

All-male tilapias are desirable because they manifest superior growth characteristics compared to females. The synthetic steroid, 17 -methyltestosterone (MT) has been commonly used to sex-reverse tilapia but because of its potential health and environmental hazards, the use of phytochemicals as alternative means to affect sex differentiation has to be explored. We addressed objective 1 by using the high performance liquid chromatography (HPLC) technique to determine MT concentrations in the water and in fish. We determined the rate of excretion/degradation of MT following dietary uptake. We addressed objective 2 by examining the dietary intake of quercetin, genistein, and complex of flavonoids in the form of maca meal or "propolis". The phytochemicals that we tested in this study showed potential for affecting sex ratios although their potency was lower compared to MT. Further studies are needed to evaluate other phytochemicals that contain flavonoids and/or isoflavonoids and how these substances are metabolized.
Introduction

In tilapia aquaculture, all-male populations are desirable because males demonstrate superior growth characteristics compared to females. Moreover, culture of monosex populations prevents reproduction and results in a uniform fish size. The synthetic steroid, 17 -methyltestosterone (MT) is a derivative of a male specific hormone commonly used to masculinize tilapia juveniles (Green et al., 1997; Abucay and Mair, 1997; Gale et al., 1999). The effect of MT is dependent on various factors such as dose, timing and duration of treatment, and mode of administration (Mirza and Shelton, 1988). A problem associated with the use of MT is that, at high doses or prolonged treatment, MT induces gonadal intersexuality and paradoxical feminization (Goudie et al., 1983; Solar et al., 1984; Van den Hurk et al., 1989; Blasquez
et al., 1995; Rinchard et al., 1999; Papoulias et al., 2000). Piferrer and Donaldson (1989) suggested that paradoxical feminization might be due more to aromatization than to inhibition of in vivo synthesis of androgens. However, these authors stressed that in some species both aromatization and inhibition of in vivo synthesis of androgens could be the cause. Use of synthetic steroids in fish culture is associated with potential release to environment and contamination. This alerts the public and causes concern as to the safety of the product. Therefore, alternative methods and new, safe chemicals to produce monosex populations should be considered.

17
-alkyl anabolic synthetic steroids are popular because alkylation at the 17-position prevents the rapid oral inactivation that occurs with other anabolic steroids and therefore, eliminates the need to inject the drug (Stanley et al., 1997,