Theses and Dissertations


Title: The use of chemosterilants, sex hormones, radiation, and hybridization for controlling repoduction in Tilapia species

Name: Al-Daham, Najim Kumur

Degree: PhD

Chair: Dr. E.W. Shell

Resides: FAA Library

University: Auburn

Location: Auburn, Alabama

Date: 1970

Pages: 160

Keywords: Chemosterilants,Sex Hormones,Radiation,Hybridization,Reproduction,Tilapia.

Abstract:

Four different methods for controlling reproduction in Tilapia spp. (Cichlidae) were investigated, and their effects on sex ratio, fertility, survival, and growth were evaluated. These were chemosterilization, sex hormones, irradiation, and hybridization. Specimens of T. aurea were treated with different concentrations of metepa, tris (2-methyl-l-aziridinyl) phosphine oxide, and tretamine, 2,4,6-tris (l-aziridinyl) s-triazine, for different periods. After treatment the fish were raised in plastic pools. Metepa inhibited brood production for 3 months and tretamine for 2 months when used at concentrations of 20 and 0.8 ppm, respectively. Histological changes induced by metepa included degeneration of the seminiferous tubules and swelling of the remaining tubules, and a reduction in number of oocytes in ovaries. T. aurea were treated with two sex hormones, testosterone and diethylstilbestrol, during gonadal differentiation. A sex ratio of 89% males was obtained when they were treated with 0.4 mg/l testosterone for a 12-day period, indicating that a degree of sex reversal was achieved. An improvement in female size was also observed.T. aurea fry were irradiated with doses ranging from 83 to 6,384 roentgens of cobalt-60 gamma-rays, and subsequently raised in pools. The results showed reduction in both gonadosomatic index and growth rate with increase in dosage. The 30-day LD50 was 2,000 roentgens. T. hornorum was crossed with T. aurea and with T. mossambica. The hybrids were raised in plastic pools, concrete pools, and earthen ponds. The highest percentage of males (84%) was obtained by crossing female T. hornorum x male T. aurea. Generally, all four hybrids showed higher survival rates and produced greater yields than their parent species.

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