In April 2015 a group of US, UK, Canadian and Swedish researchers including myself will be heading to the Antarctic Peninsula as part of a three year investigation of the icefish—one of nature’s great curiosities.
What is special about the icefish? Icefish have a cardiovascular system unlike anything else seen in nature, with massive hearts, colourless blood and extra wide blood vessels. They are the only known vertebrates without respiratory pigments, the stuff that make your blood red — something that was previously thought essential to vertebrate life. This gives them a ghostly white colour that gives rise to their common name.
Without haemoglobin that carries oxygen around our bodies, their blood carries about ten times less oxygen than that of other vertebrates. They have survived for millions of years in the Southern Ocean because oxygen dissolves better in cold temperatures, allowing just enough oxygen to be delivered to icefish’s organs because of the extremely cold temperatures it survives in. But this comes at a cost – while happy enough swimming around at -2oC, if you put one in your domestic refrigerator it would die of heat stroke!
An icefish larva (Credit: Uwe kils, Wikimedia Commons)
What is going to happen to the icefish? Global warming is pushing up ocean temperatures all over the globe, and the Antarctic Peninsula has risen by 3oC in the last 50 years and the West Antarctic ice sheet by more than 0.1°C/decade, making it one of the most rapidly warming places on the planet (British Antarctic Survey, http://www.antarctica.ac.uk).
Professor Stuart Egginton (University of Leeds, UK) will look at whether icefish will be able to cope with these changes. He says: “We think these wonderful fish, which are currently found in healthy numbers (and form the basis of a profitable fishery), may be facing a lethal double whammy. Their metabolism will increase in warmer seas and that will require more oxygen. At the same time, the increased temperature will mean that the amount of oxygen their blood can carry will decrease.”
Why should we care about the icefish? Of course, many species are at risk from global warming. Why should we care about icefish? Apart from the great loss that this unique species would be to the diversity of nature, describing the threat to icefish might be used as an introduction to/fascinating case study within a wider feature about the changes to Antarctic ecosystem. Icefish are seen as an excellent bioindicator for the health of the ecosystem in the Antarctic, because they represent one of the top predators in a relatively simple food web, and what happens to them will likely be replicated in other, less easily studied temperature-sensitive creatures.
The icefishes physiology and biochemistry is also of interest because it represents a group of animals that produce their own antifreeze to allow life at sub-zero temperatures, and display an unusual stress response that doesn’t reply on the same mechanisms as other animals. Studies are looking at how alternative ways of controlling the cardiovascular system are used by these animals, the consequences for cold-induced increases in numbers of mitochondria (the cell’s power stations, generating chemical fuel for all activity), and how the lack of other respiratory pigments within muscle fibres (myoglobin) may affect their capacity to deal with oxidative stress.
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