Half of one side on Oscar has turned very dark to black. Has also stopped eating. First thing done was to test water, perform massive water changes every 3 days (about 80%) although numbers for ammonia, nitrite and nitrate were excellent. Tried adding garlic juice to stimulate appetite.

At the end of each 3 days there was no change.

Second option was to treat tank with Fenbendazole in event of a parasitic infection.

Third option was to treat with "quick cure". Improvement in activity but still won't eat.

Further info - Tank 90 gallon with 2 Emperor 400's for filtration.
Mechanical media has been changed.
Do not use activated carbon as it causes phosphorus spike and increase in algae as well as severe diatom blooms.
Tankmates: 1 - 4" pink convict, 1 - 12" Common Pleco (hypostomus plecostomus). Substrate is gravel.
Oscar age: approx 5 y.o.
Tank age: approx 3-4 years.
Oscar size about 14"-16 long and 4.5(+/-) tall.

TIA for any help or ideas you can shed on this. I don't want to lose him. He has always been uber aggressive and these two tankmates are the only other fish he has tolerated in "His" tank. I have tried many and none lasted more than a couple of hours and had to remove them for their health.

I have seen this before, not personally but on "another forum" and I have forgotten all I read... Necro will know. He is the one that showed me! Just hang in there, and Don't treat the tank with anything yet!

I olny know my oscar will be black and blue when he rams into the lid or decor, but that definete bruising that shows.
Waiting for Necro may be your best option.

i have read about a similar sounding occurence that happens with cichlas and in one case a festae. from what i can gather it isnt fatal to the fish but it may stay this way from now on.. heres a quote from a thread talking about this issue from another cichla forum....

"Something has damaged the fish's ability to control the chromataphores used to adjust color and pigment based on mood. Most likely a bacterial infection. The chromataphores on this side of the fish's face have defaulted to the darkest "setting" possible.

Just like humans, specific parts of the body are seperated and controlled by specific parts of the brain. That's why you are seeing a very specific line and area affected by the malady. It is NOT genetic. If it were genetic the fish would have been born this way.

I've seen this in a variety of fish over the years and it is always a specific quadrant of the fish's body that is affected. It is always very well delineated and typically affects the face. It will never get better and from now on the fish's face wil be black on that side.

As far as I know there is no known catalyst nor no known treatment."

now further in the same thread the op did state that his pbass remained in good health and after a long while did return to normal.

is it possible for you to post some pics of this discolouration on your oscar so we can use it as future reference if this malady should show up on our pages again???

hope some of this helps you...

Your description fits as far as as what I can see, it does not address the lack of eating though. That has me heavily concerned as he is on 3rd week of not eating.

Will try to post pictures later on today.

Thank you for the help.

It could just be your picture quality but the bottom pic looks like pop eye????is the eye protruding??? as for the colour fade i have never known of anything like it so am stumped.

It's just the picture. When he gets irritated at me he will pale around the eyes making them appear to protrude.

I had the exact same thing happen to one of mine. Unfortunately he died shortly thereafter. The color change was dramatic...half regular colored and from the midsection down jet black.

I haven't yet found an answer to my problem but I want to update progress. I have treated the tank (fish won't eat) with Metronidazole for 2 weeks, daily 30% water changes, and treat with Seachem "Prime" and "stressguard". Prime is a dechlorinator and will also lower or bind nitrates to make the less toxic. StressGuard is pretty much a snake oil but is supposed to help with the conditioning much like API Stress Coat or Tetra Easy Balance. Stress guard is made to compliment and not counter the use of Prime, hence my choice.

Activity is returning to normal, and appetite is picking up some. However, the coloration remains unchanged. General aggressiveness is also returning. Progress is slow but present. So I would guess that this is indeed a bacterial problem but I am not certain enough to state categorically that it is as neither of the tankmates have been affected throughout the entire ordeal.

that sounds promising... thanks for the update...