Five species of notothenioid fish live in the Southern Ocean. Sitting at the bottom of the world Antarctica is one of the harshest environments on the planet. The temperature of the water can plummet to such a low temperature that many fish would freeze. But in the 1960's it was observed that these salt water fish make their own 'antifreeze' proteins that bind to ice crystals in the fish and prevent its body parts from crystalizing and freezing.
Ever since then some scientists have been curious to find out the basic genetics that allows the fish to survive.
This is the first time the genome of an Antarctic notothenioid fish has been studied to see how it's able to be so hardy. The largest species in the Southern Ocean is Dissostichus mawsoni, the Antarctic tooth fish, and researchers studied its basic genetics to look for clues.
The work was carried out by University of Illinois professor Christina Cheng and colleagues at the Chinese Academy of Sciences and the results were published in the Proceedings of the National Academy of Sciences.
To try and get a grips on the basic genetics underlying 'antifreeze' proteins the scientists looked at gene expression in four tissues; the brain, liver, head kidney (blood-forming organ) and ovary. They wanted to know which genes were being translated into proteins at high levels. They figured that proteins and genes would be expressed at high levels in cold environments.
Their genetic analysis of these tissues was compared with gene expression in the exact same tissues in fish that live in warm waters. They discovered that many of the genes that were highly expressed in the Antarctic fish were not elevated in warm-water fish.
Further to this, they analyzed the genes and found that some of them coded for proteins that respond to environmental stress, such as heat shock proteins which protect other proteins from extremes of heat and cold.
The scientists also compared the frequency of these Antarctic fish genes, with the three families of notothenioids that have never lived in icy waters. They found that these upregulated genes appeared in far greater numbers than in their warm-water cousins. In some cases they were duplicated in very high numbers. The scientists concluded that these greater numbers were needed to produce the requisite proteins to protect the Antarctic fish.