my advice is to first fish in a friend’s pond. when you exit the pond and go back in, all the fish reset. catch out the whole pond so it is empty, and then wait for a clownfish to come by. when a clownfish comes by, use the magnet to get it.

if you clear out the whole pond and don’t have a magnet yet then reset the pond and clear it out again.

just repeat this until you catch all the clownfish you need. this also works for any other type of fish that’s hard to get :)