Strange little fellow with 3 ventrals!

Here's a fun surprise from my last yellow PK spawn...a male with 3 ventrals!

I will be keeping him as a "wet pet" - definitely will not considered for breeding. I really wonder what may have sparked the production of an extra ventral. Ventrals are unique in that they are the last of the unpaired fins to develop, and their growth is started significantly after the development of the other fins.

He has impaired mobility in the extra ventral, but it is about the same length and width of his two normal ventrals. Otherwise, his form and color is actually pretty nice for a young male!