I have a 150G tank(72*20*24) that is filtered by 3*Rena XP3 canisters, a Magnum 350 canister, and 2 Emporer 400 power filters. The tanks levels are ammonia-0, nitrite-0, nitrate-less than 10ppm, and pH 7.2. The tank is stocked with 3 wild/domestic oscars that are between 9-10", 1*9" black shark, 2*8" tinfoil barbs, and a 8" suncat. I had a red bellied pacu that was rooming in here until he got up to about 15" and I moved him to my indoor pond...but unfortunatly the Pacu decided to leap out of the tank about a week ago...never trust aquarium hoods to keep your fish inside the tank.

But anyway, my oscars had always been really dark in color black with olive/golden marbeling with some red scales toward their bellies and white outlining on their fins. Very attractive fish, but since the Pacu has went missing 2 of the oscars have dramatically faded. They have went from black to a darker olive with lighter olive marbeling, while the other is still the same black/olive coloring. The 2 faded ones still eat and act normally, they darken up a little when they are being fed, but soon lighten back up. There really is no aggression in the tank...theyll occasionally take a run at each other but there is never any damage and I have alot of decor in the tank to break up lines of sight so I believe territory isnt an issue either.

Any change in diet?

Oscars change color for many different reasons some people even say their mood so maybe they 'miss' the pacu if that is even possible for an oscar.

Oscars will changes colour depending on mood. Maybe they a little unhappy with the changes in the tank. Removing the pacu may have upset the balance of the tank and them a little. Hopefully they will settle down in a week or so

as long as they r still eating and seem happy i wouldnt really worry,they just miss their buddy the pacu,they will get over it just give them sum time

Thanks :)I figured it was something along the lines of the Pacu being gone had upset the hierarchy in the tank, as the Pacu was the dominant fish. Ive noticed since I had some more time to watch my tank today that my Os are squabbling a big more than they used to, and the 2 light/faded ones are hanging out together while the dark one is more or less hanging by itself. Im going to do a large water change today to see if that helps them any.