A bright red-orange disk covered in white spots. It is shaped like a dinner plate that grew legs and learned to swim. This fish looks like art. The name comes from its round, moon-like shape and silvery sheen. It is a spectacular fish that appears to belong in a tropical aquarium rather than the open ocean. It grows to over a metre long. It can weigh fifty kilograms. It is a big, beautiful, bizarre creature. A fish that breaks the mold. Here is the weirdest thing about the moonfish. It has warm blood. Most fish are cold-blooded. Their body temperature matches the surrounding water. Not this one. Moonfish can elevate their body temperature above the surrounding ocean. This is a rare adaptation called endothermy. It allows them to hunt efficiently in cold, deep waters where other predators slow down. Tuna have this ability. So do some sharks. But a disk-shaped fish that looks like a floating target? That is unusual. It is a warm-blooded dinner plate. The moonfish swims with a slow, flapping motion of its long pectoral fins. It moves like a penguin flying through the water. It hunts in mid-water. It uses those red-tipped fins to stir up prey. Small fish, squid and crustaceans are on the menu. Nothing too picky. It lives in open ocean from the surface down to 500 metres. It prefers temperate and subtropical waters near current boundaries where food concentrates. In New Zealand, the moonfish is a rare visitor to northern waters. It ranges from Northland to the Bay of Plenty. It is most common in warm summers. It turns up occasionally as bycatch in tuna longline fisheries. No one targets it here. The open ocean is blue. The moonfish flaps its red fins, warm-blooded and round, hunting in the deep. The longline sets. The moonfish is caught. It does not know it is a mystery. It does not know it is warm-blooded. It just wants to eat squid. The ocean remains unexplored. The moonfish is proof.