The fish you can either sell them or make dishes with them (they can be used as ingredients in some recipes and if you cook those dishes you don't have to buy all ingredients from the refrigerator at that time; the game will steal from your inventory instead of costing you money).
For that wish, you can either by chance see your child get married on its own (can actually happen) or you'll have to take control of the child again. Since option 1 here is very rare, I would suggest you skip that wish unless you plan to move the child back in in the immediate future.