Icefish

Alright alright alright alright alright

You might be surprised to learn that there is a factual mistake in the lyrics to Outkast’s 2003 smash hit ‘Hey Ya!’. You will surely recall that the song includes a rhetorical question: ‘What’s cooler than being cool?’. And this is where the error occurs: the background singers answer with ‘Ice cold!’. But obviously, the correct answer is ‘Ice fish!’. Or can you imagine something cooler than having a core body temperature around 0°C? And yes, that is 32°F or 273°K or approximately 12 bushels and 5 ounces of cold. And sometimes temperature will even be lower than that. That’s right, Icefish are the real Sub-Zeros! Fans of the Mortal Kombat franchise will be delighted to hear that there are also Scorpion fishes. And fans of the Batman franchise must admit: Mr Freeze is just a poor mammalian version of an Icefish.

Two pathetic embarrassments compared to icefish

But I digress. Now how is it possible that Icefish (I hope by now you are even more appreciative of how aptly they have been named) and the waters they live in do not freeze, if these frequently fall below 0°C (32°F)? The case for the water is quickly explained: salt. The Antarctic oceans where these fish occur are sufficiently salty that they can cool down to about -2°C (28°F, 271°K, 75 stone and 2 yards of hot). But what about the fish? We know they cannot be as salty as the water they live in! And indeed, Icefish have come up with an ingenious move: their blood contains special proteins that stop it from solidifying – biological antifreeze. I guess Icefish blood is what a Bond villain would ask for at the auto shop. Now, Icefish blood is famous for another feature, one that is more visible. Or rather: invisible! They do not have red blood cells and are the only known vertebrate with ‘white blood’. I guess white blooded Icefish would consider even the purest-blooded wizard still a mudblood… Harry Potter references, anyone? No?

what a cool fish. literally! (NY Times)

Moving on. Whether this loss of haemoglobin, the protein-iron-complex that transports oxygen in the blood of humans (the iron is what makes it red), is helpful or harmful to Icefish is still debated. Some scientists think that the increased viscosity of haemoglobin containing blood would be bad in such low temperatures. Others think that this is nonsense. What is not nonsense, however, is that Icefish can only afford to not have haemoglobin because the waters in which they live have very high oxygen levels and they possess a huge heart, pumping considerably more blood than similar sized (red blooded) fish from warmer regions. So they are not just cooler than being cool and more badass than Sub-Zero and Mr Freeze, no, they are also big-hearted! What a fish!

normal fish blood versus Icefish blood

Or I should rather say: what fishes! Because there is not just one type of Icefish. They come as a gang (of some 20 species). While the gang is united in all the adaptations to cold waters mentioned above, they also share two other traits that help in this extreme environment – they have very low metabolism and go about their business at rather sluggish pace, saving energy and expending little oxygen (one might say: they are pretty chilled, most of the time); and they are scale-less, helping them absorb oxygen through their skin. Basically, they are a chill gang of overly cool naked badasses with great hearts. I think that sums it up nicely and scientifically.