all pygo piranhas you can shoal...red bellies, super reds, caribas, pirayas and ternetzis. caribas are the most aggressive, pirayas are the biggest followed by the ternetzis. red bellies are the most common one which I'm really not a fan of. if you like red bellies...super reds have better color but basically just a red belly. the piraya you saw is huge that's why it has it's own tank...hard to find a pogo that big so probably the owner could put in with his smaller pygos