Icefish or Patagonian Toothfish

a.k.a. Antarctic cod, Mero or Chilean Sea Bass.

Dark grey cod like fish on a white background
Icefish (Source Wikipedia)

Dissostichus eleginoides

This fish has a number of different names around the world. It should only be marketed in the UK as Icefish or Toothfish. 

It is a rich tasting fish, like an oilier version of Bass or Cod, and is sourced from the deep waters of the South Atlantic.

Quick guide to availability and yield

Availability of fish and shellfish. Yields of filleted fish