il pesce = the fish
i pesci = the fish
Girate i pesci should be an acceptable translation for "You (pl) turn the fish over"
isn't "the fishes" correct plural in English?
Both fish and fishes are correct. Most people use fish when they talk about a group of the same species (e.g. These fish are goldfish) and use fishes when talking about a group of different species.
http://grammarist.com/usage/fish-fishes/
Thanks, that helps!