Opah, Lampris guttatus, being photographed by a diver. This fish is able to maintain its entire body core above ambient temperature, becoming the first known fish with this trait ('whole-body endothermy'). The fish generates heat as well as propulsion with continuous movements of its pectoral fins (the musculature of which is insulated by a one-cm-thick layer of fat), and the vasculature of its gill tissue is arranged to conserve heat by a process of countercurrent heat exchange, a structure known as a rete mirabile (plural, retia).[6][7] It can consistently keep its body core approximately 5 C warmer than its environment. He also increase aerobic performance include high hematocrit and a relatively large heart, gill surface area and aerobic muscle mass. These adaptations for high performance predation are similar to those found in tuna and lamnid sharks, which actively chase down their prey, but are very unusual among lampridiform fish, which are mostly sluggish ambush predators. Azores. Composite image