They are of the opinion that the hexaploidy
may arise after spontaneous chromosome doubling in an unstable triploid fish
produced by diploid–tetraploid hybridization (Tsigenopoulos et al., 2002). In M.
anguillicaudatus, artificial hexaploidy was successfully induced by inhibiting the
second polar body extrusion after fertilization in a natural tetraploid pair (Zhang
& Arai, 1996) and through induced gynogenesis of unreduced triploid eggs of
triploid (diploid × tetraploid cross) (Arai & Mukaino, 1997).