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Grass carp was an important economic fish for freshwater aquaculture. The exploring and utilization of high-quality grass carp germplasm resources were important for ensuring a domestic supply of high-quality aquatic protein. However, natural grass carp populations in China were facing severe threats because of the effects of frequent human activities, water environment damage, overfishing, etc. Against this background, high-quality grass carp germplasm resources were the foundation for the healthy and sustainable development of the grass carp aquaculture industry, so systematic collection, preservation, identification, evaluation, protection, and utilization of them carry great strategic importance. This paper summarizes major research results of grass carp in morphology, cytogenetics, molecular population genetics, etc. It not only introduced genetic improvement techniques such as gynogenesis, hybrid breeding, and polyploid breeding, but also discussed the existing research on the protection measures of grass carp germplasm resources. On this basis, the paper proposed new methods to improve the protection of grass carp germplasm and create improved varieties, which could provide high-quality resources for the sustainable development of the grass carp industry. [ABSTRACT FROM AUTHOR]

Disease-resistant grass carp (DR-GGC) was obtained by backcrossing gynogenetic grass carp (GGC, 2n = 48, female) with common grass carp (Ctenopharyngodon idellus [GC], 2n = 48, male). The genetic constitution and the potential mutation associated with growth dominance in DR-GGC were analyzed by genomic in situ hybridization (GISH), whole-genome resequencing (WGRS) and RNA-sequencing (RNA-seq). The GISH results showed partial translocations and deletions in the chromosomes of DR-GGC compared with GC. The WGRS results demonstrated that there were numerous genetic variations between DR-GGC and its parents, among which DR-GGC had the highest genomic heterozygosity and GGC had the highest genomic purity. The RNA-seq results revealed that the differentially expressed genes (DEGs) were significantly enriched in cellular processes and immune pathways in DR-GGC and GGC compared with GC. Meanwhile, the combined analysis of WGRS and RNA-seq identified DEGs with overlapping mutation loci in DR-GGC and GGC compared with GC. These DEGs were significantly enriched in the pathways of growth, metabolism, and immunity, including cellular metabolism, biosynthesis, glycolysis/gluconeogenesis, and extra cellular matrix (ECM) receptor interactions. These results provide a genetic basis for exploring the better growth characteristics and disease resistance of DR-GGC than GC, valuable information on the genetic breeding for grass carp, and a further understanding of the genetic characteristics of gynogenetic individuals. [ABSTRACT FROM AUTHOR]