Brilliant ruby-red colouration is most intense in large adults. The ruby fish is stunning, a deep red gem of the continental slope. Large rough scales cover the body, giving a textured appearance. The bright red colour appears black in the dark waters of its deep habitat. Red is the first colour absorbed by seawater. This makes the fish effectively invisible at depth. It is a red fish that is not red where it lives. Ruby fish live in deeper water than their relative the red baitfish. They prefer rocky reefs and drop-offs on the continental slope between 50 and 300 metres down. They hover in loose schools near rocky reefs and offshore islands. Drifting prey is picked from the water column. A protrusible mouth sucks in small crustaceans and zooplankton. The feeding method is efficient for the environment. Population trends are poorly understood. That phrase again. The deep sea is vast and expensive to study. Ruby fish are caught as bycatch in deep-sea trawl and longline fisheries. These operations target hoki and other deep-water species. No one targets them specifically. They just show up in the nets. The catch is incidental. The impact is uncertain. Better species-specific data is needed for accurate stock assessments of this ruby-coloured fish. It is a brilliant red gem of the deep. It is invisible at depth. It is caught by accident. It waits for someone to learn more about its world before it is accidentally fished down. The lack of knowledge is a risk. The depth provides some protection. But not enough. That is the ruby fish. Red, rough, and invisible where it lives. A design that raises questions. The answers are in the deep. The fish continues its slow drift in the cold water. It does not know it is a mystery. It does not know it is vulnerable. It just exists in the dark. The red colour is a secret kept from the surface. Only the nets reveal it. And then it is gone. Back into the hold. Or back into the sea. Depending on the value assigned to it. Which is usually none.