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Icefishes (suborder Notothenioidei; family Channichthyidae) are the only vertebrates that lack functional haemoglobin genes and red blood cells. Here, we report a high-quality genome assembly and linkage map for the Antarctic blackfin icefish Chaenocephalus aceratus, highlighting evolved genomic features for its unique physiology. Phylogenomic analysis revealed that Antarctic fish of the teleost suborder Notothenioidei, including icefishes, diverged from the stickleback lineage about 77 million years ago and subsequently evolved cold-adapted phenotypes as the Southern Ocean cooled to sub-zero temperatures. Our results show that genes involved in protection from ice damage, including genes encoding antifreeze glycoprotein and zona pellucida proteins, are highly expanded in the icefish genome. Furthermore, genes that encode enzymes that help to control cellular redox state, including members of the sod3 and nqo1 gene families, are expanded, probably as evolutionary adaptations to the relatively high concentration of oxygen dissolved in cold Antarctic waters. In contrast, some crucial regulators of circadian homeostasis (cry and per genes) are absent from the icefish genome, suggesting compromised control of biological rhythms in the polar light environment. The availability of the icefish genome sequence will accelerate our understanding of adaptation to extreme Antarctic environments.

The complete mitochondrial genome of the Antarctic dragonfish, Parachaenichthys charcoti (Vaillant, 1906), is described, representing the first complete mitochondrial genome sequence of the family Bathydraconidae. The mitochondrial genome is 18,202 base pairs in length and encodes 13 protein-coding genes, 23 tRNAs, 2 rRNAs and 2 control regions. The overall base composition is A: 25.8%, T: 25.3%, G: 17.9% and C: 31.0%, with an A:T content of 51.1%. The complete mitochondrial genome sequence will be useful for phylogenetic, evolutionary and functional studies of Antarctic Notothenioids.

Fish are a representative population of lower vertebrates that serve as an essential link to early vertebrate evolution, and this has fueled academic interest in studying ancient vertebrate immune defense mechanisms in teleosts. Notothenia coriiceps, a typical Antarctic notothenioid teleost, has evolved to adapt to the cold and thermally stable Antarctic sea. In this study, we examined adaptive signaling pathways and immune responses to bacterial and viral pathogenic exposure in N. coriiceps. Using RNA sequencing, we investigated transcriptional differences in the liver tissues of N. coriiceps challenged with two pathogen-mimicking agonists, a bacterial ligand (heat-killed Escherichia coli, HKEB) and a viral ligand (polyinosinic:polycytidylic acid, Poly I:C). We found that 567 unique genes were up-regulated two-fold in the HKEB-exposed group, whereas 392 unique genes, including 124 immune-relevant genes, were up-regulated two-fold in the Poly I:C-exposed group. A KEGG pathway analysis of the 124 immune-relevant genes revealed that they exhibited major features of antigen processing and presentation bacterial ligand exposure, but they were down-regulated after viral ligand exposure. A quantitative real time RT-PCR analysis revealed that TNFα and TNF2, major inducers of apoptosis, were highly up-regulated after exposure to the viral ligand but not the bacterial ligand. The results suggest that the bacterial and viral ligands up-regulate inducers of different immune mechanisms in N. coriiceps liver tissue. N. coriiceps has an immune response defense strategy that uses antigen presentation against bacterial infection, but it may use a different defense, such as TNF-mediated apoptosis, against viral infection. The specific immune responses of N. coriiceps may be adaptations to the Antarctic environment and pathogens. These results will help define the characteristics of Antarctic fish and increase our understanding of their immune response mechanisms., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The striped notothen Trematomus hansoni is an Antarctic fish species belonging to the family Nototheniidae (cod icefishes) that is distributed throughout the Southern Ocean. In this study, the complete mitochondrial genome of T. hansoni was sequenced using an Illumina MiSeq platform. The circular mitochondrial genome is 19,218 bp long and contains 13 protein-coding genes, 23 tRNA genes, two rRNA genes, and one control region. Notably, there are two trnG-UCC genes and the second gene, located between trnE-UUC and trnI-GAU, has no D-arm structure. The base composition is 56.18% of A + T and 43.82% of G + C. The phylogenetic analysis supports that T. hansoni is grouped into a single clade with T. bernacchii. This study will be a valuable resource for further research on the phylogeny and evolution of the genus Trematomus. [ABSTRACT FROM AUTHOR]

The humped rockcod, Gobionotothen gibberifrons, is an Antarctic fish of the genus Gobionotothen in the family Nototheniidae and order Perciformes. To date, little biological information has been recorded about the genus Gobionotothen. Here, we report the first complete mitogenome of the genus Gobionotothen. The mitochondrial genome of G. gibberifrons is 18,631 bp in length, comprising 13 protein-coding genes, 24 tRNA genes (trnP-UGG and trnT-UGU were duplicated), 2 rRNA genes, and non-coding control regions. The base composition was 53.74% for A + T and 46.26% for G + C. This new mitochondrial genome of G. gibberifrons provides basic information for further phylogenetic analysis, suggesting the necessity to exploit a variety of newly discovered mitogenome sequences to infer inconclusive evolutionary relationships in Antarctic fishes. [ABSTRACT FROM AUTHOR]