Jin-Hyoung Kim

Having evolved in the chronically cold and thermally stable waters of the Southern Ocean (SO) for millions of years, Antarctic fish possess a suite of physiological specializations that enable them to survive at temperatures near the freezing point of seawater. Adaptations include the evolution of antifreeze proteins, modifications of membrane composition, altered metabolic processes, unique mechanisms of oxygen transport and utilization, and distinctive cellular stress responses. This review synthesizes current knowledge of the physiological adaptations of Antarctic fish, focusing on the mechanisms that support survival in extreme cold environments. We examine adaptations related to cold tolerance, osmoregulation, metabolism, reproduction, sensory biology and oxygen transport and discuss the evolutionary processes that have shaped these traits. We further evaluate how ongoing climate‐driven changes, including ocean warming, acidification and biological invasions, may affect Antarctic fish populations and ecosystems. Understanding the physiological foundations underlying Antarctic fish adaptation provides important insights into evolutionary responses to environmental extremes and provides a framework for predicting potential vulnerabilities of polar marine organisms in a rapidly changing world.

The Southern Ocean's permanently sub-zero temperatures and high oxygen solubility promote the formation of reactive oxygen species (ROS), thereby imposing persistent oxidative stress on its inhabitants. Antarctic notothenioid fish have evolved efficient antioxidant systems to counter this pressure. This study reports the first molecular characterisation of the cat transcript and deduced protein sequence, together with tissue-specific catalase (CAT) activity, in two Antarctic species with contrasting physiological traits: the red-blooded notothenioid Trematomus bernacchii and the haemoglobin-less icefish Chionodraco hamatus. Integrating cDNA sequencing with transcriptomic data, we reconstructed full-length cat coding sequences, performed Bayesian and maximum-likelihood phylogenetic analyses, and compared electrostatic surface properties using structural modelling. The cat transcript levels and CAT activity were quantified in liver, gills, heart, and skeletal muscle. Catalytic, NADPH-binding, and substrate-channel residues were fully conserved across Antarctic and non-Antarctic teleosts, consistent with strong purifying selection. T. bernacchii displayed a markedly more negative electrostatic surface than the icefish and non-Antarctic species, suggesting enhanced H2O2 recruitment linked to oxidative burden rather than temperature alone. The icefish showed a near-neutral electrostatic profile, consistent with its haemoglobin-less physiology. The liver was the principal site of both cat transcript accumulation and CAT activity in both species. Non-hepatic tissues showed a translation index below unity, indicating post-transcriptional regulation, with maximum translational efficiency shifting from the liver in T. bernacchii to the heart in C. hamatus. These findings show how enzyme surface electrostatics and tissue-specific translational regulation jointly contribute to antioxidant homeostasis under extreme marine conditions.

Curvularins, a class of macrocyclic lactones, have cytotoxic, antimicrobial, and anti-inflammatory properties. Curvularin, a 12-membered macrolactone, was used as a scaffold to design and synthesize structurally modified analogues to investigate structure–activity relationships and improve biological efficacy. Three series of curvularin-based analogues, Cur-5H-OMe, Cur-4P-OMe, and Cur-OMe, were synthesized with the same core structure but different substituent sizes and positions. Nine representative derivatives were evaluated for anti-inflammatory, anticancer, antibacterial, and antifungal activities. In LPS-stimulated RAW 264.7 macrophages, most compounds inhibited nitric oxide (NO) production in a concentration-dependent manner but exhibited cytotoxicity at high concentrations. Cytotoxicity assays against HaCaT cells and human cancer cell lines (HCT116, HeLa, and A375) revealed limited selectivity toward cancer cells. Antimicrobial evaluation indicated selective activity against the Gram-positive bacteria, Staphylococcus aureus. Compound 23 exhibited superior antibacterial potency compared with kanamycin and notable antifungal activity against Candida albicans. This study provides a versatile synthetic platform and identifies key structural features of curvularin derivatives, demonstrating their potential as anti-inflammatory and antimicrobial lead compounds.

Length-weight relationships (LWR) and Fulton’s condition factors ( K ) of two notothenioid species, Notothenia rossii and Notothenia coriiceps , were assessed using 295 and 148 specimens, respectively. Fish samples were collected from two different locations: the wharf of the King Sejong Station and Chotdaebawi in Maxwell Bay, King George Island, from January to February 2023. The coefficient of determination ( R ² ) of linear regressions on LWR ranged from 0.935 to 0.970, and the b values ranged from 3.05 to 3.27. Only N. coriiceps caught in the wharf exhibited positive allometric growth, while N. coriiceps from Chotdaebawi and N. rossii from both locations demonstrated isometric growth. The estimated condition factors ( K ) indicated that all groups of N. rossii and N. coriiceps exhibited favorable growth conditions in their respective biotopes. These findings enhance our understanding of the similarities and differences in fundamental biological characteristics, ecological aspects, and growth conditions of two important congeneric Antarctic fish species.

Nanoplastics have been recognized as emerging pollutants posing potential risks to ecosystems and human health. They are now detected ubiquitously in the environment and even human tissues, where their small size allows for tissue accumulation and cellular penetration. Growing evidence links nanoplastics to oxidative stress, yet the specific contribution of extracellular accumulation to toxicity remains poorly understood. To address this, we used zebrafish, a transparent vertebrate model suitable for toxicological studies, to explore the role of extracellular antioxidant defenses in polystyrene nanoplastic (PSNP)-induced oxidative stress. In particular, we focused on superoxide dismutase 3 (SOD3), which is an enzyme that regulates extracellular reactive oxygen species by catalyzing the detoxification of superoxide radicals. Zebrafish Sod3a is a homolog of human SOD3, preserving conserved metal-binding sites critical for enzymatic function. We established sod3a mutant zebrafish and examined their responses following PSNP exposure. In sod3a mutant larvae, tissue accumulation of PSNPs was higher than in wild-type (WT), and this was associated with elevated oxidative stress, enhanced cell death, and abnormalities in intestinal function and immune responses. Collectively, these observations reveal the functional importance of SOD3 during PSNP-induced oxidative stress and provide new insight into extracellular antioxidant mechanisms that mitigate PSNP-induced toxicity.

The white-blooded Antarctic icefishes is a representative organism that survive under the stenothermal conditions of the Southern Ocean without the hemoglobin genes. To compensate for inefficient oxygen transport, distinct features such as increased heart size, greater blood volume, and reduced hematocrit density enhance the amount of dissolved oxygen and the velocity of blood flow. Here, we investigated these unique characteristics by comparing high-quality genomic data between white-blooded and red-blooded fishes and identified the loss of FAAP20, which is implicated in anemia. Although the gene region containing FAAP20 is conserved in notothenioids as shown through collinear analysis, only remnants of FAAP20 persist in several icefish species. Additionally, we observed the loss of SOAT1, which plays a pivotal role in cholesterol metabolism, providing a clue for further investigations into the unique mitochondrial form of the icefish. The loss of FAAP20, which is known to reduce erythrocyte counts under stress conditions in mice and humans, may provide a clue to understanding the genomic characteristics related to oxygen supply, such as low hematocrit, in Antarctic icefishes.

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.

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.