I have been looking up the fat content of fish and seafood to see what has a good fat to protein ratio. It looks like Chilean Sea Bass is top of the heap, followed by salmon, yellow-fin tuna, and mackerel. Rainbow trout also has a respectable fat ratio. Shellfish are mostly protein, so cook them with lots of butter!
Steelhead trout is decent, too.
To generalize, I think that cold-water fish have a higher fat content than those from warm waters. The fattier fish usually have a stronger taste, too, versus the more mild warm-water types.
Oh good! 'Cos it’s “Fish Friday” and I’m thawing out some Scottish Salmon. It’s pretty darn fatty but I think part of that is because it’s farm raised.
If one adds the wrinkle of cost per lb etc. Mackerel can be super macro and cost efficient and is available smoked and long lasting (and super tasty). It seems a lot cheaper in Britain than the US, not sure about the rest of the world. I guess cost efficiency will depend on where you are and what is cheap locally.