Ubatuba Aquarium is a practical stop in Itaguá, close to the central waterfront and restaurants. It is not the reason to travel to Ubatuba, but it rounds out the town well: tanks, marine displays, and education work give families something useful to do between beach time and dinner.
It works best on a rainy afternoon or after visiting Projeto Tamar, when the two places together give a better sense of the sea life just offshore.