One Fish, Two Fish, Are you sure?

You may have seen this (popular) Children book:

While this isn't much of a story some kids may find this book interesting.

Ok, look at its title, just HOW can a book get the title wrong. The number two demands plural.. so it should be two fishes!

I argue with my 4 year old that it should be fishes but I stand corrected. Both fish and fishes are ok. See here. Can you think of another word that has multiple plural forms?