opah, enormous and vivid in open ocean

Size
Length: 80–120 cm, Weight: 10–25 kg
Lifespan
8–12 years
Diet
Small fish, squid and crustaceans. Hunts in mid-water using large, circular body. Uses red-tipped pectoral fins to stir up prey. Swims with slow, flapping motion like a penguin.
Habitat
Open ocean waters from surface down to 500 metres depth. Prefers cold, productive waters of Southern Ocean. Often found near current boundaries and upwelling zones where prey concentrates.
Range
Southern Ocean and subantarctic waters. In New Zealand found around Campbell Plateau and subantarctic islands. Rare visitor to mainland New Zealand waters. Occasional northward movement.
Endemism
Native
Main Threats
Bycatch in tuna longline fisheries is primary threat. No targeted commercial fishery in New Zealand waters. Climate change affecting prey distribution in Southern Ocean. Warming may reduce habitat.
Population
Global population trends poorly understood due to offshore habitat. Caught occasionally as bycatch in subantarctic longline fisheries. Rare visitor to mainland waters. Better data collection needed.
Conservation Status
Not Threatened
A silver disk with bright red fins. It floats like a painted dinner plate in the cold waters of the Southern Ocean. A fish that looks like art. The opah is a spectacular specimen. It is a close relative of the moonfish but lacks the spots. The body is smooth. The flanks are unmarked. It is a clean, elegant design. It looks like it belongs on a wall rather than in the water. But it belongs in the water. It has a secret: warm blood. A fish that heats itself. Like its spotted cousin, the opah can elevate its body temperature above the surrounding water. This endothermy allows it to hunt efficiently in the frigid Southern Ocean. Most predators slow down and become sluggish there. The opah does not. It swims with a slow flapping motion of its long pectoral fins. It moves like a penguin flying through the water. Not fast, but steady. Not aggressive, but effective. The movement is hypnotic. The result is lethal for prey. The opah lives around the Campbell Plateau and the subantarctic islands. These waters are far south of mainland New Zealand. It is a rare visitor to North Island waters. It turns up occasionally when conditions are right. It feeds on small fish, squid and crustaceans. It uses those red-tipped pectoral fins to stir up prey from the mid-water column. The fins are tools. They are also advertisements. The colour warns of nothing. It simply exists. Global population trends are poorly understood. That phrase appears again. The Southern Ocean is vast. It is expensive to study. The opah is caught occasionally as bycatch in subantarctic longline fisheries. No one targets it directly. Climate change may reduce its available habitat as the Southern Ocean warms. The water changes. The fish adapts or it does not. There is no middle ground. The Southern Ocean is cold. The opah flaps its red fins. It is warm-blooded and silver. It hunts in the frigid water. The longline sets. The opah is caught. It does not know it is beautiful. It does not know it is warm-blooded. It just wants to eat squid. Most of the ocean remains unexplored. The opah knows that. It lives there. The disk shape is efficient. It reduces drag. The red fins provide lift. They also generate heat. The biology is complex. The appearance is simple. A silver circle. A flash of red. The deep water hides most of this. We see only what surfaces. Or what is caught. The opah is not common in nets. It is not common in sight. It is a ghost of the southern depths. A warm ghost in a cold sea. It keeps going.