The Betta genus includes greater than 50 defined species. Most of them can be kept in aquariums but it is just a few species that are frequently kept by other aquarists than the true Betta enthusiasts. One of the most commonly kept Betta species apart from the Siamese Fighting fish is Betta imbellis – the Peaceful Betta. The Peaceful Betta is native to Malaysia and might reach a greatest size of 8 centimeters 3 inches. As the name indicates, it is a docile fish in comparison to the Siamese Fighting fish and the Peaceful Betta can do well in a group aquarium with other tranquil and non competitive species. 5 7.