Nice find! Reminds me of the time when as a child I went on holiday and found a pretty small one myself, though many times bigger than the one you found. It was probably something like 3 cm x 2 cm in size. Still pretty small, I'd say.

With the right aquarium set up you could keep that as a pet. I imagine they must be fairly hardy and happy to eat pretty much anything. Once it reaches full size either release or serve it up (I don't know if all species are edible but the ones I've had were all delicious so I'd like to think most should be fine if raised hygienically).

You going to release it then? ;)