Induction of interspecific allo-tetraploids of Megalobrama amblycephala♀×Megalobrama terminalis♂ by heat shock

Interspecific allo-tetraploidy was induced by a combination of hybridization of Megalobrama amblycephala ♀× Megalobrama terminalis ♂ and thermal shock. A thermal shock at 40 °C for 2 min applied to eggs 33 or 26 min (τ₀: 1.40) after fertilization resulted in a significantly ( P <0.01) higher yield of allo-tetraploids than hybrid crosses without heat shock. The yield of allo-tetraploids in embryos from mid-gastrula to hatching stages was 15.7–24.4% in different thermal shock treatment groups. The allo-tetraploidy rate in 330-day-old juveniles was 9.3% and 6.7% in different year treatment groups. After 2 years of rearing, allo-tetraploidy males attained sexual maturity with milk-like milt at the age of 2+, while allo-tetraploidy females at the age of 2+, and even at 3+, did not show any signs of sexual maturation exhibiting obviously delayed maturity. Only a few allo-tetraploidy females (three individuals) showed maturation characters at the age of 4+ and these females were induced to spawn.