No. One correct plural of the noun fish is "fishes" (also a form of the verb to fish).
You would need to add an apostrophe (fish's) to form the possessive.
fishs eddy
NO
deers or fishs
bass, bream,
The Indian & Pacific Oceans .
chalk goby
His fish are named Brock and Swimmy
Gills
what do fish eat
Increases the fish's volume by filling the swim bladder with oxygen.
dams cause many fishs' life cycle
This is not a Betta question so it belongs elsewhere.