rich oily flesh, deep-water and elusive

Size
Length: 1–1.5 m, Weight: 15–30 kg
Lifespan
10–15 years
Diet
Feeds on small fish, squid and crustaceans. Hunts in deep water using large mouth and sharp teeth. Swims with snake-like motion. Feeds throughout water column from surface to seafloor at night.
Habitat
Inhabits deep waters of continental slope between 200 and 800 metres during day. Migrates closer to surface at night to feed. Prefers warm, stable waters with strong currents for movement.
Range
Found in tropical and subtropical waters worldwide. In New Zealand it is a summer visitor to northern waters from Northland to Bay of Plenty. Most common in warm summers with high sea temperatures.
Endemism
Native
Main Threats
Bycatch in tuna longline fisheries is primary threat. Mislabelling as other fish species causes consumer issues. No targeted fishery in New Zealand waters. Climate change may expand range southward.
Population
Global populations considered stable but poorly assessed. Caught as bycatch in tropical and subtropical longline fisheries. In New Zealand it is rare visitor with no commercial importance. Flesh causes digestive problems.
Conservation Status
Not Threatened
Do not eat this fish. That is not a moral statement. It is medical advice. The oilfish contains a high proportion of wax esters. It uses these for buoyancy. Those wax esters are completely indigestible to humans. Eating oilfish causes severe diarrhoea and digestive distress. Japan has banned its sale. Italy has banned its sale. Other countries are considering it. The fish is not poisonous. It is just a laxative with fins. A fish that punishes those who eat it. The oilfish looks unremarkable. It is a deep-water predator with a dark brown body. The skin is rough and sandpaper-like. It lives between 200 and 800 metres during the day. At night, it migrates closer to the surface to feed. It hunts small fish, squid and crustaceans. It swims with a snake-like motion. Sharp teeth are always ready. It is a tropical and subtropical predator. Occasionally it visits northern New Zealand waters in warm summers. A fish that looks ordinary but is not. The problem is mislabelling. Oilfish is often sold as butterfish, cod or other harmless species. Unscrupulous sellers take advantage of the similar appearance. Buyers end up with digestive consequences they did not bargain for. In New Zealand, the oilfish is a rare visitor. It has no commercial importance. But it turns up occasionally as bycatch in tuna longline fisheries. A fish that is trouble, even when no one wants it. Global populations are considered stable, though poorly assessed. That is the standard disclaimer for deep-sea fish. It applies here too. The oilfish swims on, full of indigestible wax. It is a biological curiosity. It reminds us that not every fish is food. Some are just fish. Best admired from a distance. Best left in the water. Best not turned into dinner. The net comes up. The oilfish is caught. The fisherman sees it and sighs. It goes back over the side. It swims away, full of wax, looking for squid. It does not know it almost ruined someone's day.