I'd probably want a Staryu, and train it to become the most badass piratey Starmie around! And I shall name it, Corstar!
Although, a Carvanha would be nice too. It'll be a Jolly young fish, his name'd be Roger, he'd be fast and awesome. Another awesome piratey water pogey. He'd be victorious, he'd be fun, strong, he'd be a true Jolly Roger! *poses*