Ok, at first I thought people were feigning ignorance as a lighthearted joke.
But just in case you guys are serious, moose is both singular and plural along with sheep, deer, bison, and swine. With these words there are no separate plural forms.
Fishes is correct as a plural form but so is fish (thus fish is still both singular and plural). Other words like this are antelope, cod, salmon, elk, etc.