. Until recent times, everyone believed that only birds and mammals were fully warm-blooded. New research has shown that the Opah, also called Moonfish (Lampris Guttatus), is completely warm-blooded. This makes it one of the most scientifically documented warm-blooded fish. NOAA Fisheries scientists claim that this unusual feature provides the Opah with a competitive edge in cold ocean depths. Opah is a silvery fish with a length of two metres (6.6 feet). It can also weigh 270kg lbs. They live hundreds of feet below the surface of the ocean in cold and dimly lit water. It is very quick swimmer thanks to its long, red pectoral wings-like fins. The majority of very deep sea fish are slow and lazy and prefer to chase prey instead of ambushing it. The researchers found that Lampris guttatus is different, as reported by Science (citation below). The constant flapping of its fins keeps it warm and its metabolism quick, which gives it extremely fast reaction times. Nicholas Wegner (a fisheries biologist at NOAA Fisheries Southwest Fisheries Science Center, La Jolla in California), was the lead author. He explained that because the Opah is warm-blooded, it can swim faster, respond quicker, and has sharper vision than other deep ocean fish. Wegner stated that he was mistakenly under the impression that this fish was slow moving, as is most fish living in colder environments. It can heat its body so it is an active predator, which chases prey such as squid, and can move long distances. Wegner discovered an unusual feature in the fish’s gills. It had blood vessels that carried warm blood to its gills. These wind around the ones that transport cold blood to the body. This design is called ‘counter current heat exchange’ in engineering. It is the process where warm blood leaves the body to warm the cool blood that returns from the gills, which is where oxygen can be absorbed. It is similar to a car radiator in that it conserves heat. The unique heat exchange in the gills ensures that almost the entire fish maintains an elevated temperature, or endothermy (endothermy), even when the water is deep and cold. Wegner stated, “There’s never been anything quite like it in fish’s stomachs.” These animals have made a great innovation that will give them an advantage. Counter-current heat exchange was a concept that fish invented long before humans thought about it.” Scientists analyzed data collected from Opah during US West Coast surveys and discovered that their bodies were consistently warmer than the surrounding water. The temperature sensors were attached to fish to track prey at depths of several hundred feet. Their bodies remained stable despite diving in extremely cold and deep water. The authors discovered that the average muscle temperature of the fish was approximately 5degC higher than surrounding waters when they were swimming between 150 to 1 ,000 foot below the surface. Tuna, and some shark species warm their muscles which can increase their swimming speed. Their internal organs such as their hearts, soon become colder and they begin to slow down once they plunge into the freezing depths. This forces them back up to increase their temperature. The warmth gives the opah an advantage According to satellite tracking, the majority of opahs live between 150 depths and 1 ,300 foot without ever surfacing. Wegner stated that a higher body temperature will increase muscle output, capacity and boost eye and brain function. It also helps them to resist cold effects on their heart and other organs. The opah’s internal heat is generated by fat tissue surrounding the heart, gills and muscles. It has a constant advantage over other prey species and competitors. Recent research has revealed that there are distinct differences between opahs from various parts of the globe. Their warm-blooded characteristics are what the science team would like to compare. Wegner stated that nature has the ability to surprise us by coming up with innovative strategies when we least expect them. The cold makes it difficult to keep warm, but NOAA has been able to catch more of them off California in recent years. Scientists aren’t sure why. They believe that either their population is increasing or the current environment favors them. Although opah is not a common target for Californian fishermen, local recreational anglers have caught the fish occasionally. According to some seafood markets, the rich meat of the opah is becoming more popular. Francisco Werner is the director of Southwest Fisheries Science Center. He said that “discoveries such as this allow us to understand how species are involved in marine ecosystems and why they exist where they do.” This really shows how much you can learn from simple research on the sea, and thanks to scientists who ask good questions as to why the fish appears different. Citation: “Whole body endothermy, in a mesopelagic, fish, the Opah, Lampris Guttatus,” Nicholas C. Wegener, Owyn E. Snodgrass. Heidi Dewar. John R. Hyde. Science. Published 15 May 2015. DOI: 10.1126/science.aaa8902. Video: Opah is the first warm-blooded fish to be discovered
