I lived in Florianopolis and Curitiba. The thing about seafood is you get what you pay for, but you'll also get luckier by the beach. The seafood in Florianopolis is FANTASTIC. Curitiba is fine, but if you drive 90 mins to the Parana/Santa Catarina beaches then you can get amazing seafood.

My personal fav is camarao a grega, which is deep fried shrimp with deep fried cheese so how can it be bad?