Abstract
The research work was carried out for induction of artificial gynogenesis in the silver barb (Barbonymus gonionotus) to produce meiotic and mitotic gynogens with the view to generate monosex all-female population as the females have superior growth to males. Meiotic and mitotic gynogenesis were induced by exposing the sperm to ultraviolet light that denatured the DNA of sperm. Optimal UV-irradiation achieved when the sperm suspension containing 8×108 ml-1 was exposed to a UV dose of 196 μWcm-2 for 1.5 minutes. Diploidization of meiotic and mitotic gynogens were accomplished through cold and heat shock treatment to fertilized eggs. Early shocks prior to second meiotic division can cause retention of second polar body and produce meiotic gynogens. Mitotic gynogenesis results in fully homozygous mitotic offspring by inhibiting the first mitotic cleavage after duplication of the haploid genome. Heat shock at 40 °C for 1 minute was applied after 1.5 minutes of fertilization that produced 40.75±0.62% meiotic gynogens with their survivability of 44.07±0.43% up to yolk sac absorption stage. Similarly, heat shock at 40 °C for 1 minute applied after 27.5 minutes of fertilization produced 35.74±0.18% mitotic gynogens and their survivability up to yolk sac absorption stage was 40.90±0.37%. Cold shock at 2 °C for 10 minutes was applied after 1.5 minutes of fertilization for meiotic gynogenesis which yielded 44.23±0.62% hatching and the survival of hatchlings upto yolk sac absorption stage was 46.38±0.57%. Mitotic diploidization was done using the same cold shock after 27.5 minutes of fertilization that yielded 36.70±0.63% hatching and the survival of mitotic hatchlings up to yolk sac absorption stage was 42.16±0.65%. Haploids were produced when UV-irradiated sperm was used to fertilize eggs without applying cold or heat shock. They were deformed and died just after hatching, indicating the successful UV-irradiation of sperm. Ploidy status among all the groups were assessed by karyotype and microsatellite DNA analysis, and sexing of fish. The karyotype analysis showed the haploids to have 23 (N) chromosomes and the meiotic and mitotic gynogens and controls have 46 (2N) chromosomes. Sexing of fish demonstrated that meiotic and mitotic gynogens were nearly all-female, ranging from 98.18 to 100% and 96.43 to 100% female, respectively. The control fish contained nearly 1:1 female male. DNA microsatellite analysis revealed that the meiotic gynogenetic fry contained two alleles same as their mother and the mitotic gynogenetic fry received only one allele from mother and became homozygous. The control fry shared alleles from both of their parents. Sex-reversed meiotic and mitotic gynogenetic males (XX) were produced by feeding masculinizing hormone (17a- methyltestosterone, 30mg/kg of feed) treated feed for a period of 28 days started from first feeding stage and the sex reversed males are known as neomales. The mean survival rate of meiotic and mitotic hormone-treated gynogens, non-hormone treated meiotic and mitotic gynogens and control offspring of B. gonionotus were 49.75±0.28%, 44.28±0.32%, 61.71±0.20%, 54.24±0.24% and 67.89±0.25%, respectively, up to 28 days of rearing in aquarium. The efficacy of neomales (XX) was verified by progeny testing that produced nearly all-female, ranging from 98.10 to 100% female. When compared the growth performance of progenies of neomales (monosex all-female) with control (mixed sex), a significantly (p<0.05) higher growth was obtained from monosex all-female population. The net production of monosex all-female group (5027.18159.74 kgha-1) was significantly (p<0.05) higher than control (4094.78±89.62 kgha-1), i.e. 22.77% more production was obtained from monosex all-female population. Therefore, it is concluded that the technology developed for production of monosex all-female population of B. gonionotus is definitely promising and can be disseminated among the hatchery operators for commercial seed production.