No abstract

To predict how the shing of Antarctic tooth sh, Dissostichus mawsoni , would affect the ecosystem, it is necessary to understand the species' ecological niche. Morphological analysis of the stomach contents of 960 D . mawsoni specimens collected at depths of 946-1,600 m along the East Antarctic continental slope from December 2016 to March 2017 was used to assess dietary composition according to depth, sex, site, and size. Fishes were the most common prey item for D . mawsoni , comprising 97.8% based on the index of relative importance. Among the nine sh families consumed by D . mawsoni , Macrouridae was the dominant taxon. The size of D . mawsoni increased with depth. The dietary composition of D . mawsoni did not show signi cant differences by depth or sex, but did differ with site and size. D . mawsoni was the top predator in the ecosystem along the East Antarctic continental slope and can be considered an opportunistic feeder, feeding on abundant food in the environment. Therefore, additional studies of the diet of Antarctic tooth sh are necessary to maintain the ecosystem structure and function in a changing environment, and the results of this study can be used as a monitoring baseline.

The Antarctic toothfish, Dissostichus mawsoni , belongs to the Nototheniidae family and is distributed in sub-zero temperatures below S60° latitude in the Southern Ocean. Therefore, it is an attractive model species to study the stenothermal cold-adapted character state. In this study, we successfully generated highly contiguous genome sequences of D. mawsoni , which contained 1 062 scaffolds with a N50 length of 36.98 Mb and longest scaffold length of 46.82 Mb. Repetitive elements accounted for 40.87% of the genome. We also inferred 32 914 protein-coding genes using in silico gene prediction and transcriptome sequencing and detected splicing variants using Isoform-Sequencing (Iso-Seq), which will be invaluable resource for further exploration of the adaptation mechanisms of Antarctic toothfish. This new high-quality reference genome of D. mawsoni provides a fundamental resource for a deeper understanding of cold adaptation and conservation of species.

The habitat characteristics of Pacific cod (Gadus macrocephalus) and the ecological relationship between Pacific cod catch and environmental parameters in the southern East/Japan Sea were investigated. Pacific cod is sexually matured at age of 4-5. The highest catch of Pacific cod off the eastern Korean Peninsula occurred in seawater temperature range of 0-4°C and salinity range of 33.8-34.2 practical salinity unit at 100 m. The Cross-Correlation Function analysis showed that there was a significant negative correlation between Pacific cod catch and February seawater temperature at 75 m nearby spawning area with a time lag of 5 years in Korean waters (r = -0.360, p < 0.05). The annual catch of Pacific cod also had a significant correlation (p < 0.05) with zooplankton biomass in coastal nursery areas with a time lag, i.e., the highest ones, r = 0.432 and r = 0.452, for total zooplankton biomass in June of 5 years ago, and for euphausiids abundance in February of 4 years ago from the period when Pacific cod was caught, respectively. Furthermore, total catches of Pacific cod in the southern East/Japan Sea (i.e., sum of Korean and Japanese catches) were negatively correlated with winter Arctic Oscillation Index, and the highest negative correlation (r = -0.364, p < 0.05) was shown with a time lag of 4 years. Considering sexual maturation at ages 4-5, such statistical analyses imply that biotic and abiotic environmental factors during the early life stages of Pacific cod have a significant influence on recruitment after 4-5 years of spawning.

The complete mitochondrial genome sequence of the Icefish, Chionobathyscus dewitti was determined by the Next Generation Sequencing (NGS) analysis. The complete mitogenome was 17,452 bp in length, which encoded the canonical 13 protein-coding genes, 22 tRNAs, two rRNAs, and two non-coding regions. As shown in the other notothenids, translocation of ND6 and an additional non–coding region were identified, which is different from the typical vertebrate mitochondrial genomes. The C. dewitti was clustered distinctly from the those in the Chinodraco and Chaenocephalus , which supported the idea that this species should be classified in the different genus, Chionobathyscus in the family Channichthyidae.