>>1723900
The fish are based on the continent, one puddle on Indar is the same as all the others on Indar. In the Collections tab you can see descriptions of all the fish and it'll say what specific size they are (small, medium, large) and where they're located. You've just gotta mix and match the right bait/attractor and be in the right continent to get whatever fish you're after.

Waiting for the right place to open up is the only real pain, rest is easy enough. My robot has a bucket hat now so I'm satisfied.