the fish in this pic
"http://lh6.ggpht.com/_NRCUY6-yemE/SRUWHUkbxsI/AAAAAAAAAQE/_njIBKzU39E/s1024/P1050757.JPG
may have first ray in dorsal fin damaged and developed fungus on the wound
you may be able to catch fish out and dose the spot with iodine and acriflavine
this from another thread