Fishes are one of the most common and low-maintenance pets many people keep across the world. And despite their small size, some fish species are quite intelligent. Here we list some intelligent freshwater aquarium fishes to keep as pets:Fishes are one of the most common and low-maintenance pets many people keep across the world. And despite their small size, some fish species are quite intelligent. Here we list some intelligent freshwater aquarium fishes to keep as pets: