Oscar Diseases

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Aquarium Advice FINatic
Sep 26, 2021
I am reading up. Someone had these white lesions develop rapidly on his Oscar. I think it's Saprolegnious, aka water mold disease aka cotton wool, a fungal infection. Generally caused by poor tank management. think I'm correct?


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Saprolegnia fungus is white and fluffy (looks like white hair sticking out of the fish) and can only infect damaged tissue or open wounds. It can be treated with salt (sodium chloride). Use 1 heaped tablespoon of salt for 20 litres (5 gallon) of water. Keep salt in tank for 3-4 days after the fungus has gone. The fish in the picture does not have Saprolegnia fungus.

The white dots could be excess mucous. Fish naturally have a thin layer of clear mucous over their body and fins. It acts as a first line of defense against diseases and poor water quality or chemicals in the water. It also helps them slip through water easier. If they are injured or stressed, they produce more mucous over the damaged/ irritated area and it can appear as cream, white or grey patches or a film over part or all of their body.

Generally the first treatment for excess mucous or any unknown disease is a big daily water change and gravel cleaning the substrate, wiping the glass down and cleaning the filter. This removes a lot of pathogens and reduces nutrients in the water and can sometimes fix the issue. At the very least it buys you and the fish some time to get pictures onto a forum like this one and try to identify the problem.

If there's no improvement after a couple of water changes and gravel cleans, then add some salt.
Without more info on the fish's upkeep and a lack of a more close up picture of the area to know for sure, another possibility is the beginning stages of Lymphocystis. There's no discernable damage I can see to the area that it would be fungus. I'd follow Colin's treatment before anything else more drastic.
Thanks, Colin & Andy. Admittedly the photo lacks resolution. It was a 5.5 MB file that I shrank waaaay down on the laptop. BTW, Colin, thanks again for telling me Windows includes a nice photo editing system. Much appreciated!

I went with the top 5 Oscar diseases in researching this & cotton wool was the best fit, but incorrect. This is not my fish. My fish are asymptomatic, but I am always so grateful to learn more & pass information along to another who may benefit.
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