"Four Fish" or "Four Fishes"?

A few days ago I saw the following phrase from a book for kids:

... caught four fish.

I grinned at the low quality of the book: How can such an easy-to-spot typo allowed? "Four Fishes" not "Four Fish", please! But as I continued to read further, the same phrase appeared again in another page:

... she has four fish.

What?! Two similar typos? Hmm... I grinned no more and thought that I might be wrong!

Yes, I was wrong! I did some research and just learned the proper way to use "fish" and "fishes":

• Only one fish: use Fish;
• A quantity of fish from the same kind (i.e., many from a single species): use Fish, not Fishes! (This is the 'trap' I didn't know!)
• A quantity of fish with variety (i.e., many from more than one species): use Fishes.

Did you know about this?