Production of a novel all-male tetraploid fish via androgenesis

Male tetraploid fish exhibit significant advantages in polyploid breeding owing to their capacity for producing abundant diploid sperm to produce triploid fish. In this study, androgenesis was induced by fertilizing UV-irradiated haploid eggs (n = 50) from Japanese white crucian carp ( Carassius cuvieri , WCC, 2 n = 100) with diploid sperm (2 n = 100) obtained from autotetraploid fish (4nRR, 4 n = 200). This procedure gave rise to a diploid androgenetic population (2nAR, 2 n = 100), representing a typical cytoplasmic-nuclear hybrid that harbors cytoplasmic genetic material from WCC and nuclear genetic material from 4nRR. Notably, 2nAR is bisexual fertile and capable of producing unreduced gametes. Through the self-crossing of 2nAR, a novel all-male tetraploid fish (AM4nAR, 4 n = 200) was generated. AM4nAR reaches sexual maturity at approximately 6.5 months of age and produces abundant diploid sperm, with total sperm motility exceeding that of 4nRR, indicating robust reproductive performance and providing a valuable diploid gamete resource for polyploid fish production. Overall, this study enhances the understanding of androgenesis in polyploid fish and expands the approaches for generating all-male tetraploid fish.