Fish Injury

[crehman]

Hello All,
Last night i noticed that one of my baby Banggai cardinalfish is missing its tail. I am unsure what would have done this to it.....all that is in the tank is a clown fish, 2 other banggai cardinals and a tuexdo urchin.

The back of its body is now starting to turn brown. Is there any hope for this guy? Should i be taking him out of that tank so that i can treat it? If so what kind of medication should i use.

Any help or info would be great.