Note the teeth and large black eye in the picture at right.
Obviously a deep water predator species. I did not know the name until recently when I saw some being unloaded at Coffs Harbour fish wharf, Australia.
The young professional fishermen explained “it’s a very oily fish, you can only eat a small amount otherwise it gives you diarrhea”.
It’s called a Rudder fish.
The reason for the high oil content is to do with enabling the fish to change depths quickly without “blowing it’s air bladder”. The usual air bladder in most other fish enable them to maintain neutral buoyancy at a chosen depth pressure.
The Rudder fish uses it’s high oil content for buoyancy instead of having an air bladder.
My guess would be they hunt prey like squid from deep water at night to near the surface suffering no effect from the pressure changes.
Maybe the oil from this fish has medicinal properties? That is usually the case.
Bamboo cat sharks are alive