The other day I learnt that the world’s first truly warm-blooded fish has been discovered. I thought this was quite extraordinary, so I briefly abandoned studying to pursue my favourite hobby of Unrelated Research. And now I will present: the Opah
The opah, also known as moonfish, sunfish, redfin ocean pan and Jerusalem haddock, is a deep-sea fish thought to live most of its life in the open ocean. Little is know about this solitary creature, but recently it has been gaining popularity on the seafood menu. Like other fish, the opah breathes by drawing seawater across its gills. In coldblooded fish this flow has a cooling affect on the circulation, so that their body temperature is generally the same as that of the surrounding water, despite producing heat energy in their muscles. This year a biologist named Nicholas Wegner dissected an Opah and discovered how its gill structure was uniquely adapted to maintain endothermy. The rete mirabile (“marvellous net”) in the opah’s gills are located so as to allow a counter-current heat exchange. This means that as the seawater cools the gills, arteries carrying warm blood from the opah’s heart (which generates a lot of heat) warm the cold blood carried in the veins of the gills The opah generates most of its body heat from muscle movements and has thick, insulating fat layers to help retain it. In this way the opah is able to keep its body temperature an average of 5 degrees Celsius above the temperature of the surrounding seawater. It is thought that this slight difference in temperature gives them an increased muscle capacity, eye and brain abilities and resistance to the effect of cold on other organs.
This fascinating marine biology stuff reminds me of 20 000 Leagues Under The Sea. You can bet Jules Verne would have been all over such an amazing discovery!