Scientists Look Inside Antarctic Fish Cells to See How They Survive Near-Freezing Water

Their unusual mitochondria and recycling systems reveal the hidden costs of extreme cold.

Antarctic fish spend their entire lives in water cold enough to push cellular machinery to its limits. Yet somehow, their cells keep running.

Now, for the first time, scientists have looked inside living Antarctic fish cells at near-freezing temperatures — and found some striking adaptations.

Life at the Edge of Freezing

In near-freezing water, life should be grinding to a halt. Chemical reactions slow, proteins struggle to fold into the right shapes and the machinery inside cells has to work against physics itself.

Yet Antarctic fish spend their entire lives in water hovering around 0°C. They grow, hunt, and reproduce in conditions that would put most temperate animals under severe stress. So what, exactly, is going on inside their cells?

For the first time, scientists have captured high-resolution images of the inner workings of living Antarctic fish cells at temperatures close to those the animals naturally experience.

Researchers at the British Antarctic Survey and the University of Cambridge cultured cells from the Antarctic spiny plunderfish, Harpagifer antarcticus, and examined them with a specially modified microscope that could operate close to freezing without warming the cells far beyond their normal temperature range.

What they saw was a cell built for an unusually difficult life. The fish packed its cells with more mitochondria, many stretched into long interconnected networks, while unusually large waste-processing structures clustered around the nucleus. Together, the features hint at one of the hidden costs of surviving extreme cold: producing enough energy while constantly dealing with proteins that are more prone to folding incorrectly.

Cold Samples

The team grew cells from small pieces of plunderfish skin and fin at 2°C, then compared them with cells from the shanny, Lipophrys pholis, a temperate fish found around Britain. Researchers also established cultures from ovarian tissue and embryos, creating a new experimental system for studying Antarctic fish at the cellular level.

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The microscope itself grew out of a 2025 microscopy system developed by members of the same group. Its modifications keep cold-adapted samples near their normal temperatures without sacrificing the resolution needed to watch structures inside living cells.

Earlier work had already hinted at the problem the researchers would encounter. A 2024 comparison of the same two fish species found that, at 3°C, tissue protein synthesis was significantly lower in the Antarctic fish than in the shanny. Cold interferes with the molecular processes needed to make proteins and the delicate process by which chains of amino acids fold into working shapes.

“A misfolded protein is useless at best, but can be really harmful, so these cold-adapted cells need ways of dealing with them,” Francesca van Tartwijk, a cell biologist at BAS and Cambridge who led the research, said in a British Antarctic Survey statement.

Different Powerhouses

The new images suggest what some of those ways might be.

Plunderfish cells contained significantly more mitochondrial material than shanny cells. In skin cells, many mitochondria were unusually elongated and branched, forming what the researchers call a “hyperfused” network. The authors suggest this could compensate for the energetic challenges of living in extreme cold or help protect mitochondrial function, though those explanations are not confirmed.

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Around the nucleus, meanwhile, the researchers found enlarged acidic bodies involved in cellular digestion. The largest may be autolysosomes, structures that help dismantle damaged components. Their enlargement could reflect slower cellular digestion in the cold, a heavier load of misfolded proteins, or both.

Yet the cells were not simply sluggish. Mitochondria in the Antarctic fish moved at roughly the same speeds as those in the temperate species. They were statistically slightly faster, but the effect was so small that the authors caution it may have little biological significance.

A Costly Specialization

Antarctic animals are famous for slow growth and development. The findings suggest those whole-body rhythms cannot be explained by assuming that everything inside their cells simply operates in slow motion.

The work may also have implications beyond polar biology.

One of the central challenges these cells appear to face is protein misfolding. Proteins have to fold into precise shapes to work properly, and extreme cold can disrupt the processes involved in producing and folding them. Antarctic fish may compensate, at least in part, through changes to cellular machinery for producing energy and clearing damaged material.

That same basic problem appears in human disease. In disorders such as Alzheimer’s and Parkinson’s, misfolded proteins can accumulate and damage cells. The researchers are not suggesting Antarctic fish hold a cure, but their cells could provide a comparative model for studying how living systems cope with persistent protein-folding stress.

The findings may also help scientists probe why animals exquisitely adapted to cold often struggle with warming. Previous experiments on Antarctic fishes have found upper thermal limits substantially below those of fishes from warmer waters, although some species can increase their heat tolerance after acclimation.

The question now is where those limits begin. They might arise partly inside cells, from protein-handling and energy systems specialized for extreme cold. Or they could emerge at the whole-animal level, through systems such as circulation and oxygen delivery.

The new experiments cannot yet distinguish between those possibilities. But they finally give researchers a way to watch living Antarctic cells respond rather than infer their behavior from fixed tissue or whole animals. That could reveal not only how life became so finely tuned to near-freezing seas, but also what those adaptations can teach us about cellular stress — and where they begin to fail as the planet warms.

The preprint of the study is available on bioRxiv.