Blister and eye mark on Firefish

[Antnee]

I just noticed there is a blister on the side of one of my firefish. I uploaded a picture maybe someone could help diagnose whats wrong with the little fella.

<a href="http://s46.photobucket.com/albums/f143/zeitlin1/?action=view&current=Picture001.jpg" target="_blank"><img src="http://i46.photobucket.com/albums/f143/zeitlin1/Picture001.jpg" border="0" alt="Photobucket"></a>

There are 3 other firefish in the tank with him they show no signs of ill health.

<a href="http://s46.photobucket.com/albums/f143/zeitlin1/?action=view&current=Picture003.jpg" target="_blank"><img src="http://i46.photobucket.com/albums/f143/zeitlin1/Picture003.jpg" border="0" alt="Photobucket"></a>