Black lining on bichir rear fin

[jdryden]

I was at the local Petsmart last night staring at the bichirs they had and I noticed one had a black lining on the lower side of its tail fin. What would cause this?

 

[BichirAddict]

Have black marks when young. Nice lookin senegal in your avatar

 

[jdryden]

Thanks, thats my first bichir. I couldn't have asked for a better shot. I just picked up a gorgeous delhezi today, can't wait to get him out and into the quarantine tank. I'll post pics as soon as I do.

 

[Druu]

I was at the local Petsmart last night staring at the bichirs they had and I noticed one had a black lining on the lower side of its tail fin. What would cause this?

That's what I spent yesterday doing too. Tempting to get another one!