Oily Blackmouth is used for crafting a reagent used via Alchemy. Some of those crafted materials are still used, so this fish can still net you a decent amount of gold. And if not decent, then at least it's known for selling.
Raw Loch Frenzy can only be found in open water within the alliance zone of Loch Modan. As such, there's really only one lake to fish in, just watch out for the Modan Monster. He can be a challenge for low levels.
Before I began fishing more than I used to, I didn't think much of fishing around the Darkmoon Faire. I figured that place was all about the carnival rides and games and ticket collections.
Firefin Snapper is a bit odd in the fact that it doesn't actually help you out in cooking, but in alchemy instead. They can also be found not only in the schools dedicated to them, but also the mixed ocean school as well.
Stonescale Eels are used for making an Alchemy reagent. Certainly not as useful as the fish you may be looking for now, but they still have their place.