Otocinclus With Big White Spot

[BBrain]

Can anyone identify this white spot on my Oto's back?

Here it is when I first noticed it, on Sept.12th. It's the tiny white spot behind and above the right eye. If you look closely, there is a tiny white thread hanging off it:

Here it is 5 days later (yesterday):

Tank size: 24 gal.
pH: 7.5
ammonia: 0
nitrite: 0
tank temp: 26 C

Fish Symptoms:
White spot on back. First noticed Sept.12, has grown larger. No fuzziness/fungus. Behaviour seems normal.

Volume and Frequency of water changes: 10 to 20% every 7 to 10 days

Chemical Additives or Media in your tank: Aquaclear 50 HOB filter with foam, Biomax, and floss

Tank inhabitants: 6 Corydorus, 5 Otocinclus, 1 Bolivian Ram, 12 juvenile Endler's Livebearers

Recent additions to your tank (living or decoration): 5 of the Cories, 4 of the Otos (including the one with the white spot), and the 1 Ram

Exposure to chemicals: Regular doses of plant fertilizers (Flourish Comprehensive, Iron, and Excel)

Thanks in advance!

 

[darkleo]

It is possible that this is an injury; it is a new one to me.

 

[BBrain]

Yes, it does look like an injury, I think. Except that it has grown larger. I can't figure that out. I've seen injuries grow larger, but with fungus. This white area looks clean.

 

[darkleo]

Fungi(?) usually shoot up in 2-3 days, you can tell with one look that on some fish that it is going to be a fungus. Another thing the patch could be is an infection with a parasite or bacteria.

 

[BBrain]

I agree; fungus grows very quickly. That's the one thing I've been watching for, but there is none.
At first, that tiny white thread hanging off the white spot said "parasite" to me. But that thread is gone now, and the white spot has grown. So far, I haven't used any tank chemical treatment. I don't want to stress all the fish unless necessary. One thing I have been doing is vacuuming the crud off the bottom of the tank every day or two, just to keep the fish's environment clean. And a few days ago, I gave the Oto a salt bath in a separate container, in case it was a parasite.

But I really need to know what this white thing is, so I can treat accordingly.

 

[BBrain]

Today the white spot is larger, and the fish is less active and hanging on the glass at the surface.

I got a close look at the spot, using a magnifying glass. It looks like the skin is missing. Still no fungus.

Any help would be appreciated.

Thanks in advance.

 

[WILDER]

Big spots like that which look like you have marked them with tip x can mean parasite to bacterial.
If the fish is not flicking I would treat it as bacterial.
Good luck.

 

[BBrain]

Wilder, thank you. The fish was not flicking, so I guess it "was" bacterial. "Was", because I came home today to find it dead. Here is a photo, in case it helps anyone else with a similar problem. You can see some pink and some slimyness now, so to me, it looks bacterial:

 

[WILDER]

Bless him that nasty, sorry R.I.P.
Just keep an eye on the other fish for any signs of flicking and rubbing.
Good luck.