It's hip to be a Square Spot Fish in Happy Aquarium
According to Happy Aquarium, their new Square Spot Fish "Works hard, parties harder!", but in the real world, these fish are sensitive to light, and need plenty of hiding space to adjust to a new home.
Square Spot Fish are also hermaphrodites. They start off as females, but can swap between male and female, depending on the sex of the fish around them. Oh, and they're called "Square Spot" or "Squareback" because they sport a colored square on their sides.