Parasites? ID Please

[BuzzIIIG]

I found there is a white tentacle thing right under the fin on my powder blue tang.

Tank background:

I tore down the tank 4 months ago. Removed all sands and water, and let it dry for 2 months because one of my other fishes was sick (black spots/holes on one of the fishes). I moved all the fishes to quarantine. Treated them with Coppersafe for 30 days, and then API General Cure for 14 days, and Seachem KanaPlex for another 14 days. Since then, they were still living in the quarantine tank for a month or so after all the treatments. The Power blue tang was fine the whole time.

Since everything was back to normal, I started putting all the fishes back to the main tank after it is cycled. The tank is 2 months old. They have been back in the tank for 2 weeks and I found this on the powder blue tang a few days ago. He is eating well but seems a little bit intense(swimming very fast most of the time and not stop). The white tentacle thing is getting larger and larger. I am not sure what that is. Please help to id. Thanks

 

[Jay Hemdal]

I'm not sure what that is. It isn't a "worm" despite being worm shaped. One thing that can produce white extensions like this are copepod egg cases, from a female parasite buried under the fish's skin. However, I only see that in newly captured fish. Also, this seems less rigid than the egg case would be. Tangs sometimes have mucus producing pores go haywire and begin extruding mucus plugs. This material has the correct consistency for that, but it is too long I think, most of the plugs I see are shorter and more pyramid shaped.
You might be tempted to try and remove it, but I wouldn't - trying to catch that fish will cause it more damage than any single filament like this would.

Sorry I couldn't give you a definitive answer, but I would just "wait and see".

jay