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Cyst on lip of leopard danio, please help!


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Hi all,

The tank is roughly 10 gallons (42 litres) and planted, I've got 4 female guppy's, 3 leopard Danios (was 4), 1 baby pleco and some (6) guppy fry. 

I treated the tank for fin for with aquarium salt roughly 2 weeks ago, I've done 2 30% weekly water changes since dosing. The fish all look healthy and aren't showing any signs of fin rot anymore and look all healed up.

I did the second water change on Thursday and then Friday evening I noticed one of my Danios had died, his belly was open and looked as though it had ruptured. I checked the fish after the water change and watched them eat, they all looked healthy (including the danio that died and there were no signs of dropsy or a large stomach so no indication of what caused this death). I checked the water parameters and they are all good (ammonia -0ppm, nitrites - 0.25ppm and nitrates 10ppm).

Today, when feeding the fish I noticed one of the Danios had what looked like a cyst/blister on its lip that appeared out of no where. None of the other fish are showing any indication of this ( I've included images to help).

Sorry if the images aren't very clear, this is the best I could do with the danio they're so quick!

Does anyone know what could have caused this and how I should treat it?


Also should I isolate the danio or treat the whole tank?


Thank you 🙂




Edited by KingKyuubii
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With my danios I left for 3 days and came back to one ripped open danio. This is because the fish had not eaten in 2 or three days. For your sick danio I would use salt for a few more days. If it does nothing get a hospital tank on hand and treat that one danio with salt or meds and maybe lower or raise the temp in the aquarium depending on what sickness it has. Other than that I dont have much expirience with cysts.

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Thanks for the help everyone, checked on the cyst today and it looks like it's gone down which I'm hoping is a good sign but I'll monitor it and probably keep treating with salt if it gets worse.

I feed them every day once a day and make sure they eat but it may be a possibility that they ate the other one.

The water parameters and they are all good (ammonia -0ppm, nitrites - 0.25ppm and nitrates 10ppm).

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I think it’s a good idea to keep treating with salt if the cyst doesn’t go away. I’m not sure about the danio, but sometimes these things happen for reasons we can’t control (like the equivalent of a heart attack for fish). It wouldn’t surprise me if the other fish started nibbling on him unfortunately. Even if you are feeding them plenty, fish usually can’t resist a free meal.

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