Fellow AKA members,

I am having a problem with my A. australe BSWG-97/24, I have 8 in a moderatly planted 20 gallon standard tank, water temp 74 dgF, 100 tds (controlled), ph 8.2.  From day one I've been having a problem with very black patches on the fish, doesn't seem to bother them very much, however, it does look quite bad.  begins at the mouth goes across the top of the head back to just beyond the gills.  Rarely is it seen on the back half of the fish.  I've tried the standard treatments for "velvet" to no avail...  any help or direction is appreciated.  I'll attempt to photograph and submit a photo too...   thanks sincerely JP Langan

I've seen this. Genetic predisposition to a melanoma is what I've heard. Try breeding it out, or starting with different stock. Fairly common in AUS as everyone breeds everything and imo doesn't cull enough.

None of the adults show this characteristic, and fish from the sources say they dont have it in their fry.  Being the fish don't develop with it, it comes much later, I never considered it genetic...  I will ask the member from the DKG if he's experienced this problem since he is the original source of my population.

I do have  a lot of cynobacteria in some of my tanks... I was leaning more in that direction.

If I'm understanding correctly, the black marks are in a similar pattern on each affected fish, do not protrude from or break the skin, and do not appear to affect fish health at least in the short term?  This would not seem like an external parasitic or bacterial infection; it sounds like something is causing the fish to mess with its color cells. 

Melanoma is certainly a possibility, but I would look for  possible sources of stress as well.  I've had customers trade in angelfish with similar markings, and we believe it results from long term stress from crowding.

Since you mentioned " a lot of cyanobacteria", I wouldn't rule out the toxins that can accumulate in those tanks.