So I started with a plain white lantern (turned sideways), some card stock, and some streamers. I cut some eye and fins from the card stock and hot glued them to the lantern.
Then I cut some streamers and glued them to the back opening as a tail. This left the other opening as a very big mouth!
I cut down some blank note cards to make small number cards. I put the number 0-10 on the cards. I also used a pencil eraser to stamp dots of each number on some cards too. I made a total of 4 sets of cards (2 sets with numbers and 2 sets with dots).
I also made larger cards to hang from the mouth of the fish.
The rule of the game is they have to feed the fish 2 cards at a time that equal the large number hanging from the fishes mouth. So for the number 4 they have to feed the fish combinations of 0 and 4, 1 and 3, or 2 and 2. It may be possible to play as a competitive game as well. With players starting with a certain number of cards and drawing more if they do not have something to feed the fish. However I think you would have to remove any cards that don't work with the number on the fish. It may be more viable for larger numbers.
Of course this can be reversed and used for subtraction as well. So for 4 they would feed the fish combinations of 10 and 6, 9 and 5, 8 and 4, 7 and 3, 6 and 1, 5 and 1, or 4 and 0. I am sure it could be used for multiplication and division and possibly spelling. We'll see how long it lasts!