Hoki is often accepted as a good alternative to Cod or Haddock.
My friend runs a restaurant, and like you, they are concerened by the depleating cod stocks, so offer Hoki instead.
My local Sainsbury's even sell Hoki fish-fingers, next to the cod ones.
The following info is taken from the Waitrose website;
"Hoki
Hoki is a member of the hake family and is sometimes referred to as blue hake (it has a blue-green skin with a silver coloured underside), it has a firm white flesh that flakes easily and has few bones. It is native to New Zealand and the average size is 65 to 100cm although they can be as long as 130cm. Hoki prime fillet (skinless and boneless) is sold in Waitrose.
Uses: Hoki can be cooked in the same way as cod or haddock, it is ideal for frying, baking and grilling, it is also good in pies, fish cakes and bakes.
To store: Refrigerate hoki prime fillet as soon as possible after purchase, either in the original wrapping or in a sealed airtight plastic container, and eat within 24 hours. Fish can be frozen for up to 3 months, thaw thoroughly in the fridge before use and never refreeze fish that has been previously frozen.
To cook: To shallow fry hoki prime fillet, heat a little oil and butter in a frying pan and cook for 3 to 4 minutes on each side.
To grill or barbecue, place fillet under a medium-hot preheated grill or over barbecue coals, brush the fish with a little olive oil (try one of the flavoured oils available in Waitrose) and cook for 3 to 5 minutes on each side. If cooking on a barbecue then extra care is needed.
To bake hoki, wrap the fish in foil or greaseproof paper with fresh herbs, lemon slices and seasoning and place in a roasting tin. Bake in a preheated oven at 180�C, gas mark 4 for 15-20 minutes (check your recipe for specific timings). "