Induction of diploid gynogenesis in Micropterus salmoides using irradiated heterogeneous sperm from Siniperca chuatsi

The artificial induction of gynogenesis in fish breeding can be used to produce monosex populations. Micropterus salmoides (largemouth bass) is an important freshwater aquaculture fish, and the females grow faster than the males. In this study, we aimed to determine the best way to artificially induce largemouth bass spawning and identify suitable heterologous sperm donors to induce gynogenetic largemouth bass by suppressing extrusion of the second polar body in fertilized eggs. With respect to the artificial induction of spawning in LB, four groups were tested for hormone types. The results showed that a single intramuscular injection of the hormone combination HCG (2000 IU/kg) + LHRH-A2 (20 μg/kg) + DOM (5 mg/kg) into female largemouth bass could yield desirable spawning results, and the mean number of eggs per female in kg was 28,780 ± 4574. With respect to suitable sperm donors, largemouth bass eggs were fertilized with sperm from five fish species, and it was found that mandarin fish (Siniperca Chuatsi) sperm can activate the development of largemouth bass eggs, but most of the embryos died during development, which indicated that mandarin fish are the potential of suitable heterologous sperm donors for gynogenetic experiments with largemouth bass. The suitable optimal induction conditions were detected for chromosome doubling. The results indicated that the most effective method for promoting gynogenesis in largemouth bass was to expose inseminated eggs to a temperature of 3 °C for 15 min, beginning 2 min after fertilization. In addition, the DNA content, karyotype and morphological characteristics of the the gynogenetic larvae were consistent with those of the largemouth bass. Examination of sex-specific markers and artificial propagation of the gynogenetic largemouth bass revealed that all the tested fishes were female, indicating female homogamety (XX) in the largemouth bass. In summary, in this study, we established an improved artificial spawning technique for largemouth bass and successfully induced diploid gynogenetic largemouth bass using irradiated heterogeneous sperm from mandarin fish. Our study lays a foundation for the mono-sex breeding of largemouth bass.