Ploidy polymorphism and morphological variation among reciprocal hybrids by Megalobrama amblycephala × Tinca tinca

Highly ploidy polymorphism was detected in embryos of inter-subfamily hybridization by a cross of Megalobrama amblycephala ♀ × Tinca tinca ♂. It produced an average of 23% haploids, 46.4% aneuploids, 24.6% 2n hybrid, 2.8% 3n hybrid, 3.2% hypo-4n, which are all inviable, and also a small number of viable 2n gynogens. However, different results were found in the reciprocal hybridization by T. tinca ♀ × M. amblycephala ♂. An average of 89.1% embryos were 2n hybrids with 48 chromosomes and 6% and 2.8% of embryos were aneuploids and allo-triploids, respectively. Additionally, a proper ratio of spontaneously complete tetraploidy embryos (about 2%) was able to be induced in the reciprocal hybridization. 50% of reciprocal hybrid embryos developed normally and 30% of the normal fry survived. Ploidy polymorphism (2n, 3n, 4n or 4n mosaics) and morphological variation were identified in 120-day survival of juveniles in the reciprocal hybridization.