Successful application of UV-irradiated rainbow trout (Oncorhynchus mykiss) spermatozoa to induce gynogenetic development of the European grayling (Thymallus thymallus)

In fish with the XX/XY sex determination system, the production of all-female offspring within one generation was achieved by gynogenesis. Successful induction of gynogenesis in the European grayling (Thymallus thymallus) (Salmonidae) included egg activation with UV-irradiated homologous (996 J/m2) and heterologous (rainbow trout) sperm (1370 J/m2) followed by exposure of the inseminated eggs to a high hydrostatic pressure (HHP) shock (9000 psi for 5 min) 20 min after their activation. The survival rates of the gynogenotic larvae at the swim-up stage exhibited a huge inter-clutch variability that ranged from 1.12 ± 0.53% to 14.15 ± 1.27% and from 0.96 ± 0.33% to 60.57 ± 1.85% when the eggs were activated by UV-irradiated homologous and heterologous sperm, respectively. Maternal inheritance was only confirmed in the gynogenotes that hatched from eggs inseminated by inactivated heterologous sperm, whereas an admixture of the paternal DNA was detected among screened individuals that originated from eggs activated by homologous sperm. All the examined gynogenotes produced using heterologous sperm were confirmed to be genetically females. In the case of fish with an admixture of the paternal DNA, male genotypes and phenotypes were observed. One of the genetic males had well developed testes. Differences in the ratio of deformed larvae that hatched from eggs activated by UV-irradiated homologous and heterologous sperm were nonsignificant. Based on the obtained results, it has to be stated that the activation of grayling eggs with UV-irradiated rainbow trout sperm followed by HHP shock is a reliable and fast method for the production of all-female grayling stocks.