Best Substitutes for Firm White Fish

Hi, I am hoping for a generalized hard and fast rule for substituting firm white fish (are there unfirm white fish?). Specifically I am looking at Vietnamese Turmeric Fish, which calls for tilapia, but stating that other firm white fish will do. Would catfish, rockfish or mahi mahi fall into this category (easiest versions to get fresh ((first two)) or frozen, respectively). How would flat fish like flounder fall into this?

While I am asking, what about freshwater fish like walleye, bass or trout?

Thanks.