The third pattern, found in B. melanurus, has the caudal fin completely dark. The coloration pattern is useful for separating species, but apparently does not allow inferences about phylogenetic relationships to be safely made, since this character is widespread in this family.
A specific third pattern, present in B. melanurus, features an all-black caudal fin. This pattern serves to distinguish between species; however, it does not offer a reliable means of inferring phylogenetic relationships, since this trait is common throughout the genus.