Black Crust-like Pigmentation On Widow Tetras

[akudewan]

Hi,

I noticed that 2 of my Widow tetras have black crust-like pigmentation. Its near the gills and the chin area.

I did a web search, and found something called black spot disease. However, this looks quite different. The black marks are more like a "layer" on the skin.

The fish don't seem to be stressed in any way.

Here's the fish with the "chin" area affected:

And here's the one with the gills affected. Some portion of it is also inside the slit of the gill:

I have one more widow tetra, and some other tetras, that are unaffected.

Ammonia and nitrites are at zero. Nitrates keep varying, (its a planted tank). pH is about 6.7.

Any idea what this can be ?

 

[GuppyDude]

Could it possibly be the fishes natural pigment? sometimes when fish are stressed they have a tendancy to fade a bit, and become darker once they are more comfortable. Or has there been like a slow growth or build-up of this black pigment? Iv never seen any kind of illment that looks like this before, and if i was not told otherwise id probably say that it's the fish's natural pigment, but you definately know the fish better than i do. How long have you had him?

 

[sylvia]

I don't think there's anything wrong with them either. It looks like their normal color. It does look a lot more 'matt' than the rest but that may simply be because it's new growth - balck widows can be quite nippy with each other and this might be areas where the scales were nipped off earlier or something simialr along those lines If they are acting normal, there realy isn't anything to worry about yet.

 

[akudewan]

This doesn't look like the natural pigment to me. The Widows fade their colour when I switch on the lights, but this black portion remains jet black, it doesn't fade.

I haven't seen this build up over a period of time, it has appeared all of a sudden. Fortunately they don't seem to be stressed by it.

Any other ideas ?