The arapaima is native to the Amazon River in South America and is one of the world’s largest predatory fish. Its scales are said to be as impenetrable as armor. And it’s ugly, at least to most people. “I think it’s kind of cool,” said Captain Josh Constantine, who has been fishing the waters near the Caloosahatchee River for more than 20 years, and has been a guide for his business, Caloosahatchee Cowboys Charters, for more than a decade.