Current State of Fish Reference Genome and Pangenome: Methodologies, Sampling Strategies, Quality Assessment and...

Genome research has dominated life sciences research in the last two decades. Of approximately 11,000 sequenced vertebrate genomes, genomes of teleost fish represent about 30%, with reference genome sequences available for most aquaculture fish species. While such progress has accelerated progress in aquaculture genetics research and breeding, it is clear that understanding of full genomic variations among aquaculture species is lacking. This is largely because of the way reference genomic sequences were produced, with a single or just a few genomes being sequenced. In addition, haplotype variations and their representation in the species or population are unknown. This hinders understanding of genomic basis of phenotypic variations relevant to performance and production traits such as growth rates, feed conversion efficiency, disease resistance, stress responses, processing yields, and reproductive traits, among other traits, especially so with strain-specific performance traits. The pangenome refers to a whole collection of genomic sequences found in the entire species or population rather than in a single individual, as represented in reference genomes. Pangenome includes the core genome sequence that are shared in all individuals, and variable or dispensable genome sequence found in a subset of individuals, representing intraspecies genomic variations. In this review, we present the current state of reference genomes and reference pangenomes, compare the advantages and disadvantages of various methods in producing pangenomes, propose the concept of pangenome plus (pangenome⁺) to include genomes of related species with which interspecific hybrids can be made to introgress the beneficial genes. Revealing full genomic variations, determination of genomic variations relevant to performance traits, and combining beneficial genes and alleles into aquaculture breeds are three most important steps for the application of genome-based technologies to aquaculture breeding. To accomplish these three steps is challenging but offers unprecedented opportunities for aquaculture.