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PD/A CRSP Aquanews-Summer 2002

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Ohio State and UJAT/Mexico: Evaluating the Potency of Phytochemicals to Sex-Reverse Tilapia

by Konrad Dabrowski, Mary Ann G. Abiado, Gustavo Rodriguez Montes de Oca, The Ohio State University, and Wilfrido Contreras Sánchez, Universidad Juárez Autónoma de Tabasco, Mexico

uly 1, 2001, marked the beginning of a new CRSP project on “Studies on Fate of Methyl–testosterone and its Metabolites in Tilapia and on the Use of Phytochemicals as an Alternative Method to Produce a Monosex Population of Tilapia.”

Collaborators are Konrad Dabrowski and Mary Ann G. Abiado of The Ohio State University (OhSU), Columbus, Ohio, and Wilfrido Contreras-Sánchez and Gabriel Márquez-Couturier of Universidad Juárez Autónoma de Tabasco (UJAT), Tabasco, Mexico. The research aims to determine the concentration of methyltestosterone (MT) derivatives in tilapia and in water using radioim–munoassay (RIA) and high-perfor–mance liquid chromatography (HPLC) and to evaluate the potential action of phytochemicals on sex differentiation in tilapia.Three students from Mexico are working on the project—Gustavo Rodriguez Montes de Oca, a Ph.D. student at Ohio State, and Maria de Jesus Contreras Garcia and Guadalupe Morales Lara, undergraduate students in biology at UJAT.

Rodriguez, a Ph.D. student advised by Dabrowski at OhSU, catches tilapia for weekly sampling. The feeding study involves twelve experimental tanks provided with recirculated water under controlled
temperature (27–29ºC).
An initial study, “Phytochemical (quercetin) and Vitamin C role in Tilapia Nutrition and Sex Determination,” was conducted at OhSU and UJAT. The study sought to determine the effect of quercetin alone and with ascorbic acid on sex differentiation and growth in tilapia. Four diets—control, quercetin 1%, vitamin C (1000 ppm) and quercetin plus vitamin C (1000 ppm)—were used to feed tilapia larvae for 8 and 17 weeks at UJAT and OhSU, respectively. Mixed-sex tilapia larvae were used at UJAT while first-feeding larvae of genetically all-male tilapia (GMT, Til-Tech Aquafarm, Robert, Louisiana) were used (see experimental facility, below) at OhSU.

Results from both locations showed that the incorporation of 1% quercetin in the diet does not affect sex determination in tilapia. However, the addition of 1% quercetin and 1000 ppm vitamin C in the diet shows potential for promoting growth in tilapia. Further studies are recommended to evaluate higher percentage of quercetin in the diet.

This study demonstrated that the phytochemical quercetin has no feminizing effect on tilapia. The next step is to evaluate its masculinizing effect in a separate study using either all-female populations from FishGen Ltd, based at Swansea University, United Kingdom, or from mixed-sex populations available from fish vendors in the United States. Contreras-Sánchez will be visiting OhSU during the course of the investigation to train Rodriguez in analyzing concentrations of MT in the water and diet by RIA and HPLC. Contreras-Sánchez’ Ph.D. research at Oregon State University involved the use of these techniques for analyzing levels of MT in water and pond sediments.


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