2019-04-14 11:00:18
Ice fish were discovered in the 18th century. XIX by whalers who dared to venture into the cold and stormy waters of the Southern Ocean. Actually, it is not a fish, but a family of 16 species that inhabit the coldest oceans on Earth. Thanks to inhabiting such icy environments, “ice fish”, as they are known, can live without red blood cells and without hemoglobin in their blood, which is why it is translucent, with a slightly yellowish tint, and not red. Icefish therefore get their oxygen only by diffusion from the outside water into their blood as it passes through their gills.
However, it was not until 1929 that zoologists heard of these rare fish and did not begin to study them. To understand how such a large animal can live without hemoglobin in its blood, it is necessary to take into account at least two facts. The first is that the concentration of a dissolved gas in water increases as the temperature decreases. For this reason, it is convenient to keep carbonated drinks in the refrigerator, which delays their loss of dissolved gas. In the cold and troubled waters of the Antarctic, which can be at a temperature below 0ºC, the concentration of dissolved oxygen is, therefore, one of the highest in the planet’s oceans, which allows its diffusion into the organism of these fish in sufficient quantity.
The second fact is that the cold, well-oxygenated water environment in which icefish live means that hemoglobin is not necessary. That hemoglobin is not necessary for many of these fish that inhabit the frigid waters of the Antarctic is a fact proven by the following observation. Interestingly, some of the icefish species still possess the hemoglobin gene and produce this protein. However, if an attempt is made to poison these animals by administering cyanide, which binds to the iron in this protein and prevents it from binding to oxygen, these animals do not die. This indicates that the hemoglobin they possess is not strictly necessary to keep them alive.
To try to better understand the biology of icefish, a group of researchers has sequenced the genome of one of the species of these animals. The data from this study reveal that icefish evolved from fish in the family called sticklebacks about 77 million years ago. Another of the revealed facts is that these fish have numerous copies of genes that protect cells from freezing, producing antifreeze substances.
Other very abundant genes in its genome are those that protect against oxidative stress, probably due to the high concentrations of free oxygen, obviously not bound to hemoglobin, that exist in its blood plasma. Other genes that, curiously, are different or have disappeared in this species are those related to the maintenance of circadian rhythms, since the latitudes that these fish inhabit lack normal day and night.
These interesting studies reveal that the plasticity of life is really very high and it can successfully adapt to conditions not easily imagined. However, adaptation is not without its price and can increase the susceptibility of some species to certain changes in the environment. This is the case of ice fish and global warming, which seriously threatens to lead to the extinction of these species, not only due to effects on their diet, but also by causing their suffocation.
References:
(1) Bo-Mi Kim et al. (2019). Antarctic blackfin icefish genome reveals adaptations to extreme environments. Nature Ecology and Evolution.
(2) Johan T. Ruud. (1954) Vertebrates without erythrocytes and blood pigment. Nature, Vol 173, p. 848.
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