Mandarin losing dorsal fin?

[ThroThra]

My mandarin who is in admittedly too small of a tank (I'm looking for a new home) has been doing fine and eating pods as well as black worms and occasionally loaded brine shrimp looks like he has lost his dorsal fins. They almost look to be chewed off. What could cause this? He was all fine and dandy two days ago, yesterday it looked like the anterior had been chewed and now it looks like both have been. I'm very confused, any help would be great.

 

[Dkuhlmann]

How large is your tank and what all is in it? Also a picture is worth a thousand words...