A new type of tetraploid fish derived via female autotetraploid × male allotetraploid hybridization

Based on the production of an allotetraploid fish line (4nAL, 4n = 200, AABB, F3-F28) derived from a cross between female Carassius auratus var. red (RCC, 2n = 100, AA) and male Cyprinus carpio (COC, 2n = 100, BB) and an autotetraploid fish line (4nAU, 4n = 200, AAAA, F2-F14) derived from a cross between female RCC and male Megalobrama amblycephala (BSB, 2n = 48), we obtained a new tetraploid hybrid (4nNT, 4n = 200, AAAB) by crossing 4nAU females with 4nAL males. The aim of this study was to comparatively investigate the biological characteristics of 4nNT fish and their parents. The results regarding the DNA content and chromosome numbers indicated that 4nNT were tetraploid with three sets of RCC-derived chromosomes and one set of COC-derived chromosomes. Histological sectioning showed that female and male 4nNT individuals had normal ovarian and testis development, respectively. Analyses of 5S rDNA molecular organization revealed that the 5S rDNA of 4nNT was inherited from the original parents and contained obvious base variations and sequence insertions or deletions. The newly produced 4nNT hybrid has the potential to establish a new tetraploid fish line, and it also provides an ideal model for studying the genomic structure and genetic expression variation in polyploid hybrid fish.