Help: Two white spots on Decora

martin.a

Active Member
View Badges
Joined
Mar 28, 2026
Messages
154
Reaction score
132
Location
Canberra
What state or country do you live in
Australia
Rating - 0%
0   0   0
Please help me identify the cause of these two white spots on the dorsal side of this Nemateleotris decora, immediately adjacent to the dorsal fin. They were definitely not present yesterday. The fish appears to be behaving normally. Please tell me it's 'just trauma'. It is the only fish in the display.

Sorry for the quality of the photos and the video. I am currently fighting Amphidinium dinoflagellates, and the water is cloudy in the video because I had just stirred it up while vacuuming the sand. (The dino drama is another story... 😩)

20260926_162008(0).jpg

20260926_162005.jpg

20260926_162005(0).jpg

20260926_162140.jpg

 
Interesting the marks are bilaterally similar....seems like that would rule out another organism, pests don't typically march in line. ;) Pretty sure you're looking at skin damage from something.

Maybe others will have different ideas.

The fact that he's fat-looking and still eating are good signs no matter what.
 
Can you get him out and do a fresthwater dip? (With minimal stress?)

If it's flatworms – which is the only critter shaped about like that spot I can think of, even if one on each side directly across from one another seems very improbable – that should knock them off.

Dechlorinate some tap water in a container big enough to comfortably house the fish. Float the container in the tank or sump until it is temperature matched with the fishes tank. Then put them in the bath for 5-15 minutes...just long enough to see the spots detatch (if they do). You might be able to help them come off more quickly by gently rubbing them if the fish will allow it.

I'm still considering that it seems more like a pair of small scuffs or scrapes, but I can only see pics....you're there with him.

Can't seem to find a good example pic that's a lot like yours....this is the best I've come across, same critter but a much different fish in much worse condition, so maybe not a great comparison:
1790409536303.png
 
Can you get him out and do a fresthwater dip? (With minimal stress?)

If it's flatworms – which is the only critter shaped about like that spot I can think of, even if one on each side directly across from one another seems very improbable – that should knock them off.

Dechlorinate some tap water in a container big enough to comfortably house the fish. Float the container in the tank or sump until it is temperature matched with the fishes tank. Then put them in the bath for 5-15 minutes...just long enough to see the spots detatch (if they do). You might be able to help them come off more quickly by gently rubbing them if the fish will allow it.

I'm still considering that it seems more like a pair of small scuffs or scrapes, but I can only see pics....you're there with him.

Can't seem to find a good example pic that's a lot like yours....this is the best I've come across, same critter but a much different fish in much worse condition, so maybe not a great comparison:
1790409536303.png
Thanks, yeah, it would be really difficult to catch. I will probably give it until tomorrow before making any actions. Today fighting dinos which I first miss-identified as diatoms (which I dosed), collecting dead snakes snails and now this... Frankly, I am too shaken and tired. I know that I make errors in this state.
... And one of my phyto cultured crashed. What a day!
 
He's very sprightly....IMO he nicked himself on the live rock.

I sympathize with the lousy day...thankfully every day has its end!! :)

....speaking of which, I've had a similarly lame day and about to be done with it. 🥳🥱😴
 
I have the same fish, it has the same kind of mark on one side.
I assumed it had caught itself on a rock somewhere.... It cleared up after a few days.
 
More photos:
20260926_172434.jpg

20260926_172440.jpg

20260926_172435.jpg


There are 4 peppermint shrimps and one BTA in the tank. Plus some snails.
These are either skin irritations or scratch marks but keep an eye on area to assure healing and not becoming sore or red. If so, treat with seachem Neoplex in a separate tank
 
Try stress coat? I had one similar to that on the same fish. Looked like he hit it in rock . Fixed it in a couple days
 
Try stress coat? I had one similar to that on the same fish. Looked like he hit it in rock . Fixed it in a couple days
Stress coat is a water conditioner and not what the label name implies. Does mothing for a fish in distress
 
If you see it flashing/scratching on surfaces in the tank, I would consider that it has flukes. If not, then I would just watch it to see if these lesions heal.

You can treat for flukes with it in-tank, using praziquantel (however, I do NOT know if there is any contraindication with anything you are using to control dinos).

https://www.reef2reef.com/threads/dosing-praziquantel-pzq.1105700/
Thanks! I don't see flashing/scratching. But not seeing is not a proof of absence. 😉
I assume it must be affected by the dino toxins. It seems less hungry than normal. If these are indeed scratches, when should I see improvement?

My dino control is conservative: Dosing nitrates and phosphates to keep them 5-10/0.05-0.1 ppm, vacuuming sandbed, dosing silica and live diatoms (Chaetoceros). I don't use ozone nor UV, but I use carbon. Actually I could plumb-in UV tomorrow (Aqua 57W), but I am not sure if this makes sense... unless, I miss-identified the dinos. OK, return water sample under scope tomorrow.

The dino infestation was going OK-ish. That's why I originally assumed those were diatoms. Strombus snails liked it. No ill-effects at all. Things dramatically changed yesterday evening and escalated fast. Macro nutrients already were in the 'safe' zone. Heaps of carbon and vacuuming seemingly improved the situation.
 
Stress coat is a water conditioner and not what the label name implies. Does mothing for a fish in distress
I assumed that was a play on words, like use raincoat when it rains and stress-coat when in stress. 🙃
But indeed API makes it.
 

TOP 10 Trending Threads

WHICH PART OF YOUR SETUP IS HARDEST TO REACH OR REMOVE FOR ROUTINE MAINTENANCE?

  • Glass behind or beside the tank

    Votes: 11 20.4%
  • Powerheads or wavemakers

    Votes: 4 7.4%
  • Sump or rear filtration chambers

    Votes: 8 14.8%
  • Skimmer or other filtration equipment

    Votes: 8 14.8%
  • Overflow or plumbing

    Votes: 10 18.5%
  • Lights or lids

    Votes: 0 0.0%
  • Mine is pretty easy to access!

    Votes: 12 22.2%
  • Other—tell us what I missed

    Votes: 1 1.9%
Back
Top
Home
Post thread…
Market
What's new