I think I've found the issue

The bowl is too high. You'll have to put some rice on the bottom so it's mouth can reach.

Disclaimer: I'm not Poseidon.

There is no ginger. The fish probably feels out of place.

Maybe he's cold. Try coating the fish with algae.

Sushi by IKEA?

Pour him some fish sauce, that will bring back some good memories from when his grandma used to bake and will make him hungry again

He is just hibernating fish hibrenate during the summer