A new and a known species of Taeniacanthus Sumpf, 1871 (Copepoda, Cyclopoida, Taeniacanthidae) parasitic on Japanese fishes

Taeniacanthus aulacocephali sp. nov. recovered from Aulacocephalus temminckii Bleeker, 1855 (Serranidae) is described and T. sebastichthydis Yamaguti, 1939 collected from Sebastiscus marmoratus (Cuvier, 1829) and Sebastes inermis Cuvier, 1829 (Sebastidae) is redescribed. The male, copepodid V male, both sexes of copepodid IV, and copepodid II of the latter species are herein described for the first time.

Whole genome survey analysis and microsatellite motif identification of Sebastiscus marmoratus

The marbled rockfish Sebastiscus marmoratus is an ecologically and economically important marine fish species distributed along the northwestern Pacific coast from Japan to the Philippines. Here, next-generation sequencing was used to generate a whole genome survey dataset to provide fundamental information of its genome and develop genome-wide microsatellite markers for S. marmoratus. The genome size of S. marmoratus was estimated as approximate 800 Mb by using K-mer analyses, and its heterozygosity ratio and repeat sequence ratio were 0.17% and 39.65%, respectively. The preliminary assembled genome was nearly 609 Mb with GC content of 41.3%, and the data were used to develop microsatellite markers. A total of 191,592 microsatellite motifs were identified. The most frequent repeat motif was dinucleotide with a frequency of 76.10%, followed by 19.63% trinucleotide, 3.91% tetranucleotide, and 0.36% pentanucleotide motifs. The AC, GAG, and ATAG repeats were the most abundant motifs of dinucleotide, trinucleotide, and tetranucleotide motifs, respectively. In summary, a wide range of candidate microsatellite markers were identified and characterized in the present study using genome survey analysis. High-quality whole genome sequence based on the “Illumina+PacBio+Hi-C” strategy is warranted for further comparative genomics and evolutionary biology studies in this species.

Population genomics reveals possible genetic evidence for parallel evolution of Sebastiscus marmoratus in the northwestern Pacific Ocean

Understanding patterns of population diversity and structuring among marine populations is of great importance for evolutionary biology, and can also directly inform fisheries management and conservation. In this study, genotyping-by-sequencing was used to assess population genetic diversity and connectivity of Sebastiscus marmoratus . Based on 130 individuals sampled from 10 locations in the northwestern Pacific Ocean, we identified and genotyped 17 653 single-nucleotide polymorphisms. The patterns of genetic diversity and population differentiation suggested that the Okinawa Trough might be the ancestral centre of S. marmoratus after the Last Glacial Maximum. A shallow genetic structure was observed among sampled populations based on the implemented structuring approaches. Surprisingly, we detected genetic homogeneity in two population pairs (i.e. Xiamen–Niigata and Zhuhai–Iki Island), in which populations have large geographical and latitudinal intervals. Population structure and allele frequency distribution based on outlier loci also mirrored the observed genetic homogeneity in the above-mentioned population pairs. Integrated with biological, environmental and genomic data, our results provide possible genetic evidence for parallel evolution. Our study also provides new perspectives on the population structure of S. marmoratus , which could have important implications for sound management and conservation of this fishery species.