Sorry accidentally posted last comment under old username, didn't think expertfisherman account existed anymore. here is how i treat my Cod.
1. Gut when come ashore and wash well as sand tends to really stick if left on. I always leave head on as it makes them easier to fillet.
2. Chill them overnight or leave in chilibin with plenty of icepacks. If this is not possible at least delay filleting until the fish are nice and stiff.
3. use a really sharp filleting knife. I use a Svord carbon steel knife and a ceramic honer. I tend to rehone after every couple of fish. Victory knives are probably the stock standard and are used a lot commercially.
4. Fillet similar to a gurnard however the backbone of a red cod is curved and so the knif angle starts at a downward angle then flattens out half way through the fillet.
5. i fillet almost to the end of the tail and then flick over to skin.

Next time I am filleting a red cod I will cut a video and upload. you will see just how great these fillets can be Cheers Steve