Biologists say “fishes” when they mean multiple species of fish (http://grammarist.com/usage/fish-fishes/). Chances are they say mouses when they mean multiple species of mouse, too.
Even if they don’t, it still is valid as a word. Many people think the plural of “computer mouse” is “computer mouses”.
Even if they don’t, it still is valid as a word. Many people think the plural of “computer mouse” is “computer mouses”.