How to make fresh fish from caught fish?

[Tinile]

No vendor has fresh fish in their permanent inventory

Actually there are several merchants that always sell fresh fish. The locations were listed in this very thread above.

[Quichon]

Fresh fish may be purchased from a barbarian merchant in PoK. I know this is from inventory because I purchased them from him just after server reset and none of the merchants had purchased anything from us yet. It's in the FAR back of PoK. From Nexus stone, you go to the bank, keep going past the bank, past the entrance to the "good" side, past the library (you'll actually go UNDER the bridge to library from good side) and you'll see a merchant row. Inside is a pool and two barbarian fishermen. Also, if you look to your right, you will see a Tir'dal (dark elf) merchant who sells batwings from inventory.

This is how even an Iksar like me (in fact this is how I did it) can get his skill up to 135 and have enough "filler food" to make his stat food last a very long time indeed.

[Sylphan]

Cabilis is different than other zones. In Cabilis you catch various sizes of fetid bass instead of the normal types of fish. This is usually a good thing, provided you have enough room in your packs to store 20 different types of fetid bass, because they're good food. Funny that you got stuck with the 'better' fish when you wanted to do some baking. In almost any other zone you'd catch many fresh fish.

If you want to convert to fresh fish, I recommend you go to PoK and sell your fetid bass then buy fresh fish from the merchants there.