Looks like a chestnut oak leaf to me, but I could be wrong. I'm not aware of any North American broadleaf tree leaves that are poisonous to shrimp, but fruit tree leaves are usually frowned upon because they get sprayed with pesticides and such. If you have a fruit tree that you know for certain hasn't been sprayed for a year, shrimp love the leaves from most of those as well.
Note: My ignorance does not equal a fact.