Ailing Oscar

Question
I inherited a 100 gal. freshwater aquarium about 3 years ago and it included an Oscar. I have no idea how old the Oscar currently is but at the time I received the tank, the Oscar had already grown to his maximum size within the tank. The tank also has a few Goldfish and a Plecostimus. Of course, "Ich" seems cyclic in nature and I've been treating that w/Malachite Green & Formalin. I've also recently statred using Metronidazole for "Hole-in-the-Head" disease instead of relying on the "Ich" medicine, which did an okay job. After the last water change that took place a few days ago, my Osacr seems to have taken a turn for the worse. For the 1st couple of days after the water change, my Oscar stayed almost completely vertical, with his nose touching the rocks on the bottom & his tail fin pointing to the top of the tank. It was then I noticed that the Oscar seemed un-evenly bloated from his head, throughout his mid-section and tapering off toward his tail. He has now taken to just lying on the bottom of the tank and as far as I can tell, he has not eaten in days. To add insult to injury, the Plecostimus has taken to feeding/sucking the scales off the Osacr. So my questions are: Is my Osacr suffering from something that can be cured by medication or some other immediate action that can be taken? If not and these are indeed my Osacrs last days, can you suggest a humane way I can help my Oscar end his is suffering?

Thanks for any help you may be able to provide,

Marcus

Answer
Hi Marcus
Oscars do most of their growing their first year, then it slows down a bit.  If he's at least 12 inches, he's definitely a few years old.  They can live 10+ years.  

How often were/are you doing water changes?  
And how much water do you change out?
Do you have a test kit-and if so what's your ammonia, nitrite, and nitrate levels?  If you don't have a test kit, I'd strongly suggest buying one that tests those.
Does the oscar have HITH disease?  If not, why the metronidazole?  

The water change you did, and he was vertical, how large was the water change?  Sometimes with large water changes, if the temperature isn't right or if the ph is different from the tank, it can cause swim bladder issues.  However, that's also a sign of internal parasites.  I just think it's strange that it happened right after the water change though.  The oscar being bloated...hard to say without knowing the water quality etc.  It could be dropsy, it could be an internal bacterial infection-like hexamita, could be an internal parasite.  The best course of treatment is to use an antibacterial and/or an antiparasitic food to get the meds inside the fish.  The pleco is sucking his slime coat, and that's not good, especially if the oscar has something transmittable.  I'd suggest if you have a separate tank, move the oscar for treatment.  If not, try to make a tank divider for him.  I did that once with a 75 gallon tank, just used some plexiglass, and drilled a bunch of small holes in to allow the water to flow through.  I'm trying to help someone else with a very similiar situation, here's the link:

http://www.allexperts.com/expertx.cgi

If it doesn't work, you can look at View Past Questions by my profile/name, and it's titled My oscar is slowly dying.  It's pretty long, we've been dealing with it for awhile now, but like I said, seems to have alot of the same symptoms.  

Honestly, if he's not eating, and if it is dropsy, it's very difficult to treat.  Here's a few links for euthanizing, I also talked about it on that link, I prefer the clove oil method.  It's so far the most humane method of doing it.

http://www.wisegeek.com/what-is-the-most-humane-way-to-euthanize-a-fish.htm

http://www.petalia.com.au/templates/StoryTemplate_Process.cfm?Story_No=1885#ct-4

If you can get back with me on some of those answers, we can try to narrow it down further maybe.

Christy