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PD/A CRSP Aquanews-Summer 2001
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Athauda Defends Reproduction Control Thesis

Congratulations to A.R.S.B. Athauda, who successfully defended his masters thesis at the Asian Institute of Technology in Thailand in December 2000. Athauda, a native of Sri Lanka, returned to his home and has been accepted into a doctoral program in Australia.

Ultrasound-immersion Techniques to Improve the Efficiency of Sex Reversal of Male Tilapia Population
(abstract of A.R.S.B. Athauda’s MS thesis)

Recent studies on sex reversal have shown that immersion technique requires substantially shorter exposure period compared to feeding. The present study was conducted in order to determine the best treatment combination using immersion techniques. Furthermore, this study used ultrasound with immersion treatment to achieve high sex inversion and more consistent production of mono sex male population of Oreochromis niloticus.

The first experiment was carried out as a preliminary study to determine the best immersion duration of one or two hour as for immersion in Methyltestosterone (MT) and Androstenedione (AN) at concentrations of 100 µg/L, 500 µg/L. The second experiment was conducted with immersion solutions of Methyltestosterone (MT), Methyldihydrotestosterone (MDHT) and Trenbolone acetate (TBA) hormones with concentration levels of 50, 100 and 250 µg/L each. The third experiment was carried out with two hormones, MDHT and TBA 100 µg/L and 250 µg/L each. All the other conditions were similar to experiment two. Immersion periods of 2 h were applied for all treatment combinations of ultrasound, non-ultrasound and control.

Of the two time periods (1 h and 2 h) applied in the preliminary trial, 2 h immersion resulted in higher (91.75%) and consistent male percentage with ultrasound, while 1 h gave lower (73.5 %) and highly variable results. Both concentrations (100 µg/L, 500 µg/L) of MT and An showed similar results (83%, 82.3%) with ultrasound treatments. Between two hormones, MT resulted in higher male percentage (90.25%) with ultrasound compared to An (75%). Ultrasound immersion resulted 82.63 % males, while non-ultrasound gave 69.5%. In experiment two, ultrasound resulted in significantly higher (P< 0.05) male percentage (96%) than non-ultrasound (87.5). Highest (P< 0.05) percentage of males resulted with ultrasound treated with MT 50, MDHT 100 and TBA 250 µg/L. The male percentages were similar (97, 96, and 96). Without ultrasound treatment, percentage males were 86, 87 and 88. In experiment three, significantly higher (P< 0.05) percentage of male population was found with ultrasound (93.35%) treatments than non-ultrasound (89%) in experiment three. Highest (P< 0.05) percentage of males resulted with ultrasound treated with MDHT 100, TBA 100 and 250 µg/L. The male percentages were 91, 94 and 98, respectively. Without ultrasound treatment, percentage males were 83, 88 and 94. Furthermore rest of the treatment combinations (MT 100 µg/L, MDHT 250 µg/L) also achieved high sex reversal rate, but were not significantly different from non-ultrasound.

This study indicated that the ultrasound treatment with immersion was more effective in sex reversal of Oreochromis niloticus than treatment with immersion alone.

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