Characterization of allodiploid and allotriploid fish derived from hybridization between Cyprinus carpio haematopterus (♀) and Gobiocypris rarus (♂)

The production of hybrid progeny through distant hybridization holds great significance in enriching germplasm resources for fish breeding. In this study, a hybridization experiment was conducted between female KOC (Cyprinus carpio haematopterus) and male GR (Gobiocypris rarus), resulting in the production of two distinct types of hybrid offspring. These progenies were classified as allodiploid and allotriploid based on their DNA content and chromosome numbers, hereafter referred to as CG and CCG. Subsequently, a comprehensive comparative analysis was performed between the CG and CCG hybrids and their parents, focusing on countable traits, measurable traits, erythrocyte morphology, as well as karyogene and mitochondrial gene composition. The majority of the examined countable and measurable traits in both CG and CCG exhibited similarities predominantly with GR, except for the ratios of body length (BL) to body height (BH) and head length (HL). Moreover, observing erythrocytes revealed the presence of dumbbell-shaped nuclei in CCG, a characteristic not observed in CG hybrids or the parents. Sequencing alignment revealed that the homeobox (Hox) genes and 5S RNA in CG and CCG were inherited from both KOC and GR, signifying their status as allodiploid and allotriploid organisms. The mitochondrial genes in CG and CCG showed substantial similarity to KOC, albeit with a few sites displaying paternal leakage inheritance from GR. In comparison to CG, the growth rate of CCG was found to be significantly faster, which could be attributed to the upregulation of growth hormone 1 (gh1) and the downregulation of myostatin b (mstn). This study successfully produced two hybrid offspring with distinct growth characteristics but similar genetic backgrounds, making them ideal subjects for future investigations into growth traits. The findings of this research established a fundamental basis for investigating the growth mechanism of fish and provided significant implications for the advancement of fish breeding through hybridization.