i agree whole heartedly! Half of the rare fish I have caught just when I was wandering by my pier or river, saw a fish shadow and thought, ‘what the heck, I’ll catch this fish, wonder what it is’ - this is what really happened with several of the pier fish, and also with the barrel eye - I spent probably 40-60 baits, maybe more, because I decided I wanted to catch it. And I didn’t. And then one night while I was about to stop playing for the night I saw a small shadow off my pier and just decided to fish. And t
there is really no rush, no competition to finish your museum. It will give you more to do in the game and be more fun in the long run to still have stuff to complete.
this is the tactic I am taking with my art exhibit. I check in with Redd whenever he shows up, sometimes he has all fakes, sometimes he has real art I already have. I could trade for what I need, but I just am not too impatient to finish (there was an article that says it will probably take me 3-4 years to finish this way but oh well).
it is nice having stuff left to accomplish, and also as the quoted post says, no one cares how complete your museum is.
it sounds like trying to catch these fish the way you are is not fun, or helping you enjoy the game right now, so I would just take a break and give to a chance to happen naturally as you enjoy your game.
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—But if you really do want to keep grinding, then the mystery islands are your best bet, go to a variety of them, and look into which ones are specialized for different types of creatures!
good luck!