Population genetic structure of Antarctic toothfish, Dissostichus mawsoni from Subareas 58 and 88 (the Ross Sea and the Amundsen-Bellingshausen Sea) using microsatellites and SNPs

The Antarctic toothfish, Dissostichus mawsoni, serves as a valuable fishery resource around the Antarctic Ocean, managed by the CCAMLR since 1997. Although delimitating the population genetic structure of this species is crucial for improving the fishery conservation and management, its number of genetic populations or stocks still remain unclear. In the present study, we analyzed the level of genetic diversity and population structure of the Antarctic toothfish in Subareas 58 and 88 by using 14 microsatellites including our developed Antarctic toothfish microsatellite markers. We further performed population genomic analysis of the 58 (N = 68) and 88 (N = 54) samples of an average of 9.5 Gb per individual using approximately 218,320 SNPs (Single Nucleotide Polymorphisms). The level of microsatellite diversity tended to be higher in populations from the Ross Sea region (88.1 RBB, 88.1 RBH, 88.1 RBI, 88.1 RBK, and 88.2 SRZ) than in those from the Amundsen-Bellingshausen Sea (88.2 RB1, 88.2 RB4, 88.3 RB1, 88.3 RB2, 88.3 RB3, 88.3 RB4, 88.3 RB5 and 88.3 RB6) and also from Subarea 58. Population structure analyses suggest a well-admixed shared gene pool in Subareas 58 and 88 probably due to high ongoing gene flow during the prolonged larval phase of this fish. However, given weak, but significant microsatellite differentiation found between 42 population-pairs (58 vs. 88; 22 pairs, within 88; 20 pairs) implies the possible existence of distinct genetic stocks or groups. Although there was no difference in the genetic structure between age groups in Subarea 88 determined by otolith microchemistry, we still found some detectable differentiation between the age groups of juvenile and adolescent and spawning adults. The results of genomic SNPs showed overall well-admixed a single gene pool in Subareas 58 and 88. However, SNP-based population structure analysis exhibited the 58.4.1 population formed a unique cluster relative to the other populations (58.4.2, 58.5.2, 88.1 and 88.3). In addition, there was genomic differentiation among the five populations. The findings of this study will provide important information for making conservation efforts on the stock (unit) management for this valuable fishery resource.