Which Aniimo can swim?
18 of the 93 can swim, and 15 of those can be caught in the wild rather than raised. The dex lists the ability per creature; this is that list inverted.
Catchable now
Raised, not found
These have no habitat in the dex, which means evolving one is the route. Follow the chain back on each page.
Which one should you get?
Not answerable yet, and not answerable anywhere else either. Every Aniimo on this page clears the same obstacle, so the question is which is fastest to obtain — and that needs a measured drop rate, which does not exist for this game today, here included.
That is what we start measuring on 16 September — how it works. Nothing here is estimated.