Hello Nancy!
Some of the common fishes are easier to find, you can catch them almost anywhere with the right lure and size of inner circle (ripple, if u prefer), and it's impossible to note them all of the location in Chumley's data compilation.
But most of the rarest (and the hardest to catch) fishes are unique to a particular area.
Some of the rare fishes are:
Bitterling, can only be found in deep water
Golden Trout, can only be found in reed
Speckled Dace, deep water
Brook Trout, reed
Longear Sunfish, Reed
...and so on, I probably missed some other, and there might be people who catches the fishes above outside the specific area I mentioned. If there is, please let us/Chumleyboo knows so we can update the data!
Therefore, in my opinion, it's impossible to collect all the fishes without expanding at all. Expanding 1 of each area might be, but not at all is impossible.
- currently lv 72