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Breeding Biology and Monosex Male Seed Production of Genetically Improved Farmed Tilapia (gift) Strain of Oreochromis Niloticus L. in Bangladesh

A.H.M. Kohinoor
Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh

M.S. Islam
Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh

M.A. Mazid
Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh

M.G. Hussain
Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh

Abstract/ Executive Summary:

A study on the breeding biology of the GIFT strain of Nile tilapia, Oreochromis niloticus was conducted for a period of five months. The sex ratio of the parent individuals was optimized for performance in spawn production, where the best results were obtained with a sex ratio of female to male of 4:1 compared to those of 3:1 and 2:1. The diameter of eggs obtained from the GIFT stock had major and minor axes of 2.19±0.09 and 1.72±0.07 mm, respectively, with no significant differences between the treatments. The average number of eggs produced was 392±22 per female, with fertilization and hatching rates ranging between 94-96% and 85-88%, respectively. No significant variation was observed between the treatments. Breeding frequencies per female in the three treatment groups ranged between 10-40 days and the highest value was obtained at a female to male sex ratio of 4: l. In an other experiment, l7 alfa-Methyltestosterone (MT) was applied orally to the fry at their first feeding stage with treatments- 1, 2, 3 and 4 at the dosage of 100, 80, 60 and 40 mg/kg feed respectively, for the period of 28 days. The mean percentage of males obtained in treatments, 1, 2, 3 and 4 were 98, 97, 95 and 68, respectively. Treatments-1, 2 and 3 did not differ significantly (P>0.05) from each other but treatment 4 showed significant variation (P<0.05) from other treatments. The results showed that MT-100, 80 and 60 mg/kg feed administered for 28 days produced close to cent percent male population of the GIFT strains in aquaria.

Keywords: Breeding biology, GIFT, Monosex tilapia

Location: Freshwater Station (FS), BFRI, Mymensingh

Start Date: 00-05-2000

End Date: 00-09-2000

Program Area: Variety and Species

Commodity: Tilapia

Objectives:

To evaluate some attributes in breeding biology especially in relation to optimization of sex ratio of brood individuals in a suitable controlled breeding environment for spawning

Methodology:

The study was conducted at the Freshwater Station (FS) of the BFRI, Mymensingh for a period of five months during May to September '00. Origin of the fish stock: The GIFT strain was developed by the International Center for Living Aquatic Resources Management (ICLARM) through several generations of genetic selection from a base population involving eight different strains of Nile tilapia, O. niloticus. In on station trials, the synthetic GIFT strain was reported to show on an average 60% faster growth and 50% better survival at harvest than the most commonly farmed strains in the Philippines, the Israel strain. For evaluating this strain in other countries of Asia, a research project was initiated in five INGA member countries viz. Bangladesh, China, Philippines, Thailand and Vietnam under the auspices of a World Fish center's (Formerly ICLARM) project entitled 'Dissemination and Evaluation of Genetically Improved Tilapia Species in Asia (DEGITA)'. As a member ofiNGA, BFRI received GIFT strain during July' 94. Stocking and management of breeders : The experiment was conducted in nine nylon hap as ( 4.0 m3 each submerged in water; 3.4 m x 2.0 m x 0.6 m) over a period of five months. There were three treatments on sex ratio of broods (Female: Male) with three replicates T₁ (2:1), T₂ (3:1) and T₃ (4:1). All brood fish were PIT (Passive Integrated Transponder) tagged before initiation of the trial. All the hapas were placed in a pond (1600m²) and brood fish (80-90g) were stocked in the hapas at a density of 3 fish/m³^.All the fish were fed daily with a formulated feed (40% rice bran, 15% mustard oil cake, 30% wheat flour and 15% fish meal) at the rate of 6% of estimated body weight. The quantity of feed given to fish was adjusted every two weeks. Water quality parameters such as temperature (^oC), dissolved oxygen (mg/l) and pH of hapa water were measured between 8.00 to 9 00 AM at weekly intervals during the experimental period. Experimental procedure : The mouths of females in hapa were checked at ten days interval to observe their breeding performance. Eggs were collected from the mouth of a female and the tag number of the spent fish was recorded. The total number of eggs collected from a female was counted and the rate of fertilization of eggs was estimated through observations under stereo microscope, the dimensions of eggs (both major and minor axis) was determined with an eye piece micrometer (Olympus Compound Microscope; Olympus CHT, Olympus Optical Co., Ltd., Japan). Monosex seed production of GIFT strain: Egg collection and spawn production : Fertilized eggs collected from the mouth of a female from the breeding hapas were kept in jar (6 L) incubation system in hatchery with a water flow rate of 2 L per minute. Fry were obtained through hatching of eggs after an incubation period of 90-96 hours. The hatchlings were transferred through water flow of the jar to a metal trough with showering adjacent to the hatching jar. Fertilized eggs collected from the mouth of a female from the breeding hapas were kept in j:u (6 L) incubation system in hatchery with a water flow rate of 2 L per minute. Fry were obtained through hatching of eggs after an incubation period of 90-96 hours. The hatchlings were transferred through water flow of the jar to a metal trough with showering adjacent to the hatching jar. Hormone treatment : Six day old fry were divided into fifteen groups for five treatments with three replicates each containing 200 individuals in glass aquaria (50x23x23 cm³). The hormone 17a-Methyltestosterone was administered orally to the fry at their first feeding stage to treatments 1, 2, 3 and 4 at the dose of 100, 80, 60 and 40 mg/kg feed. Feeding was ad libitium for the first 14 days and at 10% body weight for the following 14 days. The fry of treatment 5 (control) were fed with the hormone free diet. Water in each aquaria was partially changed (30%) once daily in the morning during the removal of uneaten food and faeces. The hormone feeding was continued for a period of 28 days. Fry nursing in hapa : After hormone treatment, the different groups of treated and non-treated fry were transferred to hapas placed in a pond for further rearing with hormone free diet. During this nursing period, all the treated groups were given supplementary feed containing 30% protein at a feeding rate of 8%. After 8 weeks of rearing, all surviving fry were harvested and sexed through gonadal examination. Gonad examination : Samples of 30% of the individuals of each replicate of the treated and non-treated fish were dissected to take out the gonads to examine under a compound microscope. Acetocarmine stains was used on the slide for clear identification of the gonad. Statistical analysis: Data were analysed using the statistical package, Statgraphics Version 7. Duncan's New Multiple Range Test (DMRT) was applied to identify which treatment was different from others. Goodness-of-fit x² tests were used to assess the fit of observed numbers of males and females to a 1:1 sex ratio.

Source of Information: Bangladesh J. Fish. Res., 7(2), 2003: 105-114

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The results showed that MT-100, 80 and 60 mg/kg feed administered for 28 days produced close to cent percent male population of the GIFT strains in aquaria.

Knowledge Management: Journal