False. Fishes is plural for multiple species of the animal. Thus, "there are several fishes in the sea" (as opposed to several types of fish).
When you are numbering individual plural animals, you'd use fish. E.g., "I have four fish at home."
And as for "sleeping with the fishes," that's merely an idiomatic expression.
I guess nobody uses a dictionary anymore. The plural of fish is either "fish" or "fishes". Many of you think that because you have never heard or read something, it doesn't exist, or it is wrong. A quick consultation with Mr Merriam Webster can prevent these forums from being littered with false information.
"Sleeping with the fishes is a movie quote from an Italian American family. It makes sense that he would pluralize fish~ as that's how it's done in Italy. However, In American English it's done so seldomly as to not even be taught in school. There are several other words that are used similarly, but the one that comes to mind is deer. A deer, three deer, a family of deer.
I agree with you. My wife is Italian with a masters degree in English she was watching me doing the test and was very surprised when it came back with a wrong answer. " I have some fish" means more than one, it signifies the plural. Its a valid answer. " I have the fish" I suppose if you have a van load of fish, you could say to a shop keeper I have the fish. But considering you have one sentence with limited context, I see nothing wrong with saying some fish. .