Red Gills, Lethargy on Danios

[d6veteran]

So I've been calibrating a fairly new tank for just over 3 months and all the fish were happy until some big change this weekend.  Cory's and Plecos fine, but all 18 Danios (10 Zebra, 8 Kyathit) have gone into hiding at the bottom in the plants/driftwood, only a few come out to eat.  Just now I tried to coax them out with some food.  Several came out and I noticed red gills on at least two of them.

Internet search took me many places ... 

• Ammonia is 0, so it isn't Ammonia poisoning
• CO2 is between 15-30ppm, but the fish are not gasping for air or going to the surface
• So that leaves ... bacteria?  But why don't the Cory's and Plecos have it (at least they are acting normally with no red gills)?

My first tank crisis 😞

[RyanU]

Being new to the  l hobby I am no expert but I have done some research and May have found an answer for you on another forum. It cold be flukes Which according to what I read needs to be treated. It’s apparently common in danios but doesn’t effect other fish. Hope this helps

[d6veteran]

I did see some references to Flukes and it says look for hairs (they are worms).  I need to get a photo of the fish so I can enlarge and see if there are hairs ...

I did not see that it was common to Danios.  Thanks for the reply!

[adamh]

I’m by no means an expert and won’t comment on the cause, but I will say in my experience corys and plecos are the last ones to show signs of the problem but the first ones to struggle from medications. If you can separate them for treatment I would. One of my worst days is when I inadvertently killed a couple plecos while treating a nasty (finally figured out...I think) columnaris infection from a really popular Lfs. I still call it my “death tank” and always have regret when I look at it. Also, I totally freaked out and went crazy on treatment, which is probably the worst response. I’d use every available resource to try and really pin down what’s happening and treat appropriately.

in a pinch, you can relocate to a plastic bin with an air stone and a usb pump from Aquarium Co-op for the catfish and work on saving the danios.

 

good luck! 

[d6veteran]

Good advice.  I am going to calibrate some things in the tank that might be stressing the fish out (like low pH).  And capture one of the Danios to inspect the gills.  Then like you said, carefully form a plan.

[RyanU]

More research that I found said that all you may need to do is quarantine and add aquarium salt for a few days. But there is always an option to go with medication. Good luck hope they pull through. 

[d6veteran]

Update.  I retrieved two of the Zebra Danios and put them in a small bowl.  They both look fine.

I then fiddled with the lights to reduce the all but the blue hues (so I could still see in the tank) and then fed bug bites which drew about half the Danios out.  They were very tentative - zooming out to grab a bug bite then zooming back into hiding.  I did spot the Danio with the red gill and it looks more like a damaged gill.  I can see a bit of scale flashing just below the gill like it was torn.

Observing the other fish more closely (as best I can as they are FAST), some of the gills are pink-red, and I am wondering if this is normal and I am just looking for reasons based on their weird behavior.

I am going to hold tight and just let the tank be without any changes for a week or two.  There have been many many changes in the past 2-3 weeks (plants added, pH change, a major piece of aqua-scaping taken out and put back).  They might just be overly stressed and need some peace.