Opah, the warm-blooded fish The opah (moonfish) has a global range that includes the southern waters of Australia and swims at depths between 10 and 450 metres, and its warm-blooded Source ABC The opah, Lampris guttatus. (NOAA: Ralph Pace. ) Some fish that can warm their blood a little include some species of tuna and the Lamnidae family of sharks which includes the Great White. It’s only localised and temporary though. Recent research has shown that the opah is the only known fish species to be whole-body endothermic, or warm-blooded. Dr Nick Wegner says this trait gives the opah distinct advantages as a deep-sea predator. “It will increase its performance in cold environments – it can swim faster, has faster reaction times and better visual resolution than a lot of its prey,” It was an “opportunistic find” after blood vessels were found that “weren’t supposed to be there”. Wegner says the fish flaps its fins to produce heat. As the warm blood leaves the core and travels to the gills where it warms the blood passing through the gills. Fat also surrounds the gills, heart and muscle tissue. The researchers found the opah was able to warm up an extra 5 degrees Celsius higher than the surrounding water. Museum of Victoria senior curator of Ichthyology Dr Martin Gomon says it suggests the related southern moonfish would likely have the same feature. The southern moonfish is known to be active despite living in cold, deep waters. “The discovery just shows how little we know,” he says. Last year a moonfish washed up at Stanley on the NW coast of Tasmania, although they are more commonly seen in tropical Australia. Tagging opah, NOAA