The mouth has a hole as well, fyi.
Whole thing is selfmade, of burnt clay with outside glazing.

Do the holes connect? I'm assuming they do.

Little tin foil bowl with some pin holes for the bottom hole. (Unfortunately, you have to hold him upside down)

Then put a straw in his mouth like a snorkel. Use a little gum or play doh to create a seal in the mouth.

Ain't nothing fancy, but sounds fun to me!

Whole thing is hollow

No straw, just kiss the fish!

Somebody should definitely make similar sculptures but with whales, as they have ports on their back, and thus don't need to be flipped upside down.

I thought that too, but it doesn't feel like engineering if there's only one step.