I bought “cooked frozen food” for DIY fish food.

[Tavero]

I wouldn't feed cooked, especially since you mentioned clams/mussels and it's easy enough to get those live at any supermarket with a decent seafood counter.

On the other hand, I've used roasted nori plenty of times even though I know raw is better and everyone liked it.
*not quite the same as the main discussion, but still

Dried is definitely better because every time I open the box with roasted nori I get hungry and want to eat it myself.

(Both versions are heat treated though. So I don't think there is a lot of difference)