This macabre ice fish contains antifreeze in their veins and we now know how it works



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Have you ever wondered how fish survive in freezing temperatures in Antarctic waters? (You are now.) It's a good question – and now, thanks to the genome analysis, we have an answer.

For a fish, that's it. And the boy is strange. This is what is called the Antarctic Black-finned Icefish (Chaenocephalus aceratus), known for many peculiarities – and one in particular.

This fish and its cousins ​​Channichthyidae, originating from the Antarctic seas, do not have functional red blood cells, which are normally responsible for the transport of oxygen in the body. They are the only vertebrates known to possess this trait.

So here they are swimming in cold, icy water at temperatures below 0 degrees Celsius (32 degrees Fahrenheit), without functional hemoglobin – the protein found in red blood cells.

To compensate, they developed a huge heart, improved vascular systems and started producing antifreeze glycoproteins to lower the internal freezing temperature.

Now scientists have analyzed the fish genome to understand why these extreme adaptations have evolved.

Researchers from the Korea Polar Research Institute found that the suborder of the icefish, Notothenioidei, was different from the lineage that had produced the stickleback some 77 million years ago. Using comparative genomics, they were able to quantify the changes.

By the time Antarctica reached -1.9 degrees Celsius (25.58 degrees Fahrenheit), about 10 to 14 million years ago, the notothenioids began to diversify, producing cold-tolerant adaptations. .

"Our results show that the genes involved in protection against ice damage, including the genes encoding the antifreeze glycoprotein and zona pellucida [egg] proteins, are highly developed in the icefish genome, "the researchers wrote in their article.

"In addition, the genes encoding enzymes to control the state of cellular redox … are extensive, probably because of evolutionary adaptations to the relatively high concentration of erythrocytes. dissolved oxygen in cold Antarctic waters. "

Anti-freeze proteins protected the organisms and the ice-resistant egg proteins preserved the safety of their unchecked young children.

The analysis also revealed that some of the circadian regulatory genes had been suppressed in icefish. This suggests that the day-night cycle in Antarctica – where the sun never sets in the summer and does not rise in the winter – limits the usefulness of circadian regulation.

The selection pressures to conserve these circadian rhythm genes were probably mitigated by the fact that the fish did not use them, which allowed the genes to be degraded through mutations over time.

This will require additional research to check – to see if the ice fish is actually lacking this day-night cycle behavior, possibly including a comparison with creatures living in the Abyssopelagic, Ocean Zone. so deep that the sun can not penetrate.

Any discovery on this enigmatic ice fish will certainly help us better understand how life can adapt even to the most difficult and inhospitable environments.

"The blackfin icefish genome provides an elegant natural model for facilitating the exploration of genomic contributions to a wide range of evolutionary, ecological, metabolic, developmental, and biochemical characteristics of Antarctic fishes, as they are used in research." they adapt to the extremely low temperatures, the high oxygen rate and the highly fluctuating days in Antarctica, "the researchers wrote in their article.

"The availability of the icefish genome sequence will accelerate our understanding of adaptation to extreme Antarctic environments."

The article was published in the journal Nature Ecology & Evolution.

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