My 16 year old black used to share his tank with a female midus he grew up with. She passed away three years before we lost him in a power failure while I was out of town.
Basicly it IS possible but highly unlikely. My black was raised from a fry to almost two feet long. (Sorry no pictures. this was all well before my first digital camera.) This might have made all the differance or it might simply have been 'one of those things' In any case the two were inseperable for a LOT of years.