Establishment and application of distant hybridization technology in fish

Hybridization is widely used. However, for a long time, systematic theories and technologies related to hybridization in fish have been lacking. In this study, through long-term systematic research, we investigated and obtained the main rules regarding inheritance and reproduction related to fish distant hybridization. Furthermore, we established one-step and multistep breeding technologies that were suitable for interspecific hybridization and intraspecific hybridization. Simultaneously, we used these two breeding technologies to produce a batch of diploid fish lineages and tetraploid fish lineages and improved fishes. In addition, we widely discuss the methods, technologies and results of hybridization breeding, referring to the domestic and foreign literature on fish hybridization. We hope that this paper will be beneficial for the research and application of fish hybrid breeding.

The chimeric genes in the hybrid lineage of Carassius auratus cuvieri(♀)×Carassius auratus red var.(♂)

Hybridization can combine the genomes of different strains or species, which leads to changes of genotype and phenotype in the hybrids. In this study, we aimed to investigate the genetic variations of hybrids(WR-F1 and WR-F2) derived from the intraspecific hybridization of white crucian carp(Carassius auratus cuvieri, WCC, ♀) and red crucian carp(Carassius auratus red var., RCC, ♂). Here, we compared the orthologous genes in the liver transcriptomes of hybrids with those of WCC and RCC, and classified the orthologous genes into eight gene patterns within three categories(chimera, mutant, and biparental origin genes).The results revealed 19.04%, 4.17% chimeric genes and 6.90%, 5.05% mutations of orthologous genes in WR-F1 and WR-F2 respectively. Seventeen of twenty-three characterized genes(77%) were confirmed to be the chimeras at the genomic DNA level.The GO classification discovered that some chimeric and mutant genes were related to metabolic process, immune system and developmental process in WR-F1. Our results provide the new evidence that hybridization can combine the parental genomes,leading to changes in the genotype of the resultant hybrids. This is the first report on the formation of chimeric genes from fish intraspecific hybridization, which is potentially interesting from the context of both evolution and the genetic breeding of fish.

Abnormal meiosis in fertile and sterile triploid cyprinid fish

Meiosis is the key process for producing mature gametes. A natural fertile triploid Carassius auratus population(3nDTCC) and an artificially derived sterile triploid crucian carp(3nCC) have been previously observed, providing suitable model organisms for investigating meiosis characteristics in triploid fish. In the present study, the microstructures and ultrastructures of spermatogenesis were studied in these fishes. Td T-mediated d UTP nick end labeling detection was performed to investigate the apoptosis of spermatocytes. Fluorescence in situ hybridization was employed to trace chromatin pairing. In addition, the m RNA expressions of cell cycle-related genes(i.e., cell division control 2 and cell cycle protein B) were determined by quantitative realtime polymerase chain reaction to illustrate the molecular mechanism of abnormal meiosis in the 3nCC. The results showed that the 3nCC undergoes an irregular prophase I, with the chromosomes distributed in a unipolar radial manner and exhibiting partial pairing, hindered metaphase I, and degenerated cells in the subsequent stages. Meanwhile, the 3nDTCC presented a relatively regular meiotic prophase I with complete conjugate chromosome pairs and chromosomes distributed along the karyotheca,which were presented as a ring structure by slicing. Only the spreads with 130–150 irregular chromosomes can be easily detected in the 3nDTCC, suggesting that it may undergo an abnormal metaphase I. This study provides new insights into the meiosis of fertile and sterile triploid cyprinid fish.