It's hard because the plural form of "fish" is usually "fish." I think we allow "fishes" when "fish" is ambiguous, like my example. Maybe we should just change to "fishes" all the time :)
Deep in the weeds here, but the plural of a single species of fish is 'fish', while multiple species of fish are 'fishes'.
'Swimming with the fishes' means you must have wound up on the wrong side of a boat in a diverse body of water. It would be a shame to have to 'swim with the fish'. So ambiguous.
The plural "fish" is more than one fish of the same species. The plural "fishes" is multiple species. At least biologists make that distinction. edit: what Alex Young said.
'Swimming with the fishes' means you must have wound up on the wrong side of a boat in a diverse body of water. It would be a shame to have to 'swim with the fish'. So ambiguous.