Abstract: Ophichthus urolophus, a deep-sea benthic fish distributed in the waters around Taiwan, China, is one of the common species of family Ophichthidae. In this study, we used high-throughput sequencing technology to obtain the genomic survey data for O. urolophus, and screened microsatellite loci to analyze their composition and distribution. The results showed that the high-throughput sequencing yielded approximately 57.95 Gb of raw data, and subsequent quality filtering resulted in 332185654 high-quality reads. K-mer analysis estimated that the genome size of O. urolophus was about 2090 Mb, with the genomic heterozygosity rate being 0.75% and the proportion of repetitive sequences being 64.76%. In total, 1632962 microsatellite loci were identified, with a cumulative length of 2113854428 bp, randomly distributed across 1038185 sequences. The occurrence frequency, appearance frequency, and relative abundance of microsatellite loci were 13.91%, 21.88%, and 769.51 loci·Mb^-1, respectively. Among the six types of perfect microsatellites, dinucleotide repeats were the most prevalent, possessing the largest number (1024107, 27.52%), the highest appearance frequency (13.72%), and the greatest relative abundance (484 loci·Mb^-1). There were 2087 repeat motifs in total. Among which, hexanucleotide repeats had the highest variety of repeat motifs (1000) and mononucleotide repeats contained only 4 repeat motifs. Six dominant repeat motifs were successively A (139167, 40.93%), CA (334656, 32.68%), AAT (13067, 11.76%), CACG (7092, 5.81%), TGTAA (4510, 16.98%), and CACACG (440, 4.81%). In terms of the lengths of microsatellites, there were more medium and high-polymorphism microsatellites (Type I and Type II). In conclusion, there is a high complexity of the genome of O. urolophus and a high abundance of genomic microsatellite markers. Our results can provide data supports for the development of molecular markers and also offer references for further researches on the adaptive evolution of deep-sea fish species in the future.

Key words: Ophichthus urolophus, high-throughput sequencing, genomic survey, K-mer analysis, microsatellite