My Oscar Has Developed White Marks On His Body

Hi, I'm new to these forums, so I apologize if I'm doing something wrong.
Anyway, over the past couple of weeks, my oscar has been developing these strange white marks--almost slimy-looking. I can only see them when light is directly hitting them. I only hope this is not a precursor to HITH. He also appears to be breathing only through one side of gills--he's acting normal otherwise. Here's some info about my tank:
1 tiger oscar - 8in
1 jack dempsey - 6in (they get along surprisingly well)
90 gallon aquarium (48" x 18" x 24")
2 Marineland Emperor 400 Powerfilters (rated for 80gal aquariums each)
Temp. = 80°F
Weekly 50% water change
Ammonia = 0ppm
Nitrites = 0ppm
pH = 7-7.5
Nitrates: 0-20ppm
Diet: HikarI Cichlid Gold pellets and freeze-dried shrimp/mealworms

Is there something I'm missing here?

 

First off I thought it was fighting marks but now you have said about only one gill working says there could be something more happening, I'll give Dawn Michele a shout if she dosn't know she'll point you in the right direction

 

HI Justin!!! Welcome to Fishlore!!! IM sorry to hear about your Oscar but I don't know what the mark's are or what is going on with his breathing. CaptainAquatics might know.

 

I don’t know either sadly.... the only think I could think of for the breathing is that something injured his gills, maybe the Jack Dempsey bit his gills. Or maybe he swallowed something sharp and it exited through his gills (but that is a bit of a stretch). Sorry I don’t know, hope he gets better

 

HI Justin. I would just keep an eye on him and hopefully he will get better.

 

Thanks everyone, I appreciate your thoughts! I don't think the jack dempsey hurt my oscar, though. If anything it would be the other way around, the jack is very docile. Occasionally my oscar will chase the jack dempsey to the opposite side of the tank or nip at him, but I have never seen them directly injure each other. I think I got pretty lucky with these two. The oscar, however, injures himself all the time. He likes to ram his head into the top of the tank for no apparent reason, sometimes he runs into tank decorations, and sometimes he likes to square up with particular decorations that he feels need taught a lesson. As a result, he always seems to have some kind of scrape or two. Maybe he has some sort of infection or something? I don't know much about that stuff. Anyway, for now I am treating with aquarium salt and hoping for the best.

 

HI Justin. My Big Boy was ALWAYS ramming into thing's and getting scraped. Pristine water healed him. How is his breathing?

 

HI Justin. My Big Boy was ALWAYS ramming into thing's and getting scraped. Pristine water healed him. How is his breathing?

Nothing seems to have changed since I made my first post unfortunately. He's still only breathing through one side at the moment.

 

I wish I could help you more with your Oscar. My best to him.