Well, there is a rather archaic use of "fishes" as the plural (consider, for example, biblical references to "loaves and fishes"). "Fishes" can also be used to refer to different species of fish. (See http://www.merriam-webster.com/dictionary/fishes )
It's not often used in conversation today to refer simply to several fish. Still, if the sentence is "I am not your fish(es)" why not also be surreal and archaic?
As I often do, I forgot about fishes being used for multiple kinds of fish. That kind of thing always felt wrong to be. I shudder when someone says peoples. That being said, it's still impossible for one person to be multiple kinds of fish.
On the front of being surreal, I would love to have an entire category of all these weird surreal sentences, but one that can only be reached late in the game.
I was thinking that language influence probably goes both ways. Italy is the bordering country next to several Slavic countries in the East; it is obvious how much Italian language influenced western Slovenian dialects, but who knows, maybe Slavic languages like Slovene and Croatian influenced Italian as well, at least a little. I know for sure that Slavic languages heavily influenced Romanian language, as Romania is an island of Romantics among all Slavs, with exception of Hungarians.