Ah that is where you got Pumas from earlier on the other thread, I see, I even googled it and could find nothing.
fish can be fishes and I've heard native speakers use it that way.
Fish is plural and singular but I thought that if you mean different species you can say "Fishes", different currencies "monies" and "peoples"?.
But you are right language changes and quickly.
I remember always being corrected on "eatable" and told it was "edible" but both are in the dictionaries.