Have you looked at oriental trading?? They have a huge amount of fish-themed decorations.
You could also get the kids to do paper plate fish - one whole plate is the body, then cut a plate in half and staple/tape it to the back end as the tail like this: OC
Tie fishing poles to the corners of your booth or any posts?
My husband built our sout of three sheets of wood with two hinges connecting each piece and we painted it with chalkboard paint so we could color it with chalk according to the event. We used an ocean and fish in the spring but a field and pumpkins in the fall.
The irony of commitment is that it’s deeply liberating-in work, in play, in love. The act frees you from the tyranny of your internal critic, from the fear that likes to dress itself up and parade around as rational hesitation. To commit is to remove your head as the barrier to your life. --Anne Morris