More mysterious Cory deaths

Hi there,
I posted last month about unexplained Cory deaths - (https://www.fishforums.net/threads/help-corys-keep-dying.464480/page-2#post-3971864). Basically one by one, the Cory's would start acting strange - breathing rapidly, lying at strange angles and with some swimming oddly (sideways, spinning etc) before dying. No visible physical symptoms. This happened until one Cory remained.

I waited a couple of weeks and the cory seemed fine, however as it was now alone I was concerned and eventually purchased 4 juli corys (no delphax available, very hard to find). This was 2 weeks ago and they all seemed healthy until a couple of days ago when one Cory started showing symptoms.

I first noticed the Cory wasn't as active and was breathing more heavily. Last night it started swimming sideways and spinning, occasionally laying on its side. Gills possibly a bit red, although it's hard to tell if that's just lighting (see picture).

Tank is 50 gallons and contains 8 cardinal tetras, 7 ember tetras, 1 BN pleco, 3 amano shrimp and 5 corys.

Just tested water - 0 ammonia and nitrites, 10 Nitrate, PH around 6.5 and temp is 25c. Fed shrimp pellets, algae wafers and flake.

From suggestions in the last thread I stopped feeding Bloodworms completely, and added a powerhead for better flow. Also been vacuuming more thoroughly.

Any ideas? Should I treat for internal parasites (waterlife octozin), and if so should I treat the whole tank? Any other suggestions? I don't have a quarantine/hospital tank but am planning on purchasing one now.

Any chance of something being on your hands when you added them?

I had a recent incident of hand sanitizer which causes some spinning symptoms in my cories and a myriad of other symptoms.

So I wouldnt rule out some sort of contamination.

Pictures of the other catfish?
Video of the fish spinning through the water?

When fish spin/ spiral through the water they have a bacterial or protozoan (usually protozoan) infection in the brain.

The fish in the picture also looks like it has a microsporidian infection. This is related to protozoans and causes the muscle tissue to turn white. Pictures of the other catfish can help confirm the muscle is turning cream/ white under the skin.

If it is a microsporidian or protozoan infection then salt is the only treatment I have found that works. To treat a microsporidian infection I would normally use 4 heaped tablespoons of rock salt for 20 litres of water but the Cories and tetras won't like that. So you will need to use 2 heaped tablespoons per 20 litres and hope it works. Keep the salt in there for at least 2 weeks but no longer than 4 weeks.

Before adding salt, wipe the inside of the glass down, clean the filter, and do a 75% water change and gravel clean the substrate. Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

When you do water changes while using salt, you need to treat the new water with salt before adding it to the tank so the salinity (salt level) in the tank remains stable.

When something very similar happened to me about a year ago, it only affected the C. trilineatus shoal. Sadly, the internet didn't proffer solutions, and I lost all of them. It wasn't fast, either. They dropped off one by one, over a period of about three or four months. I had other cory species as well as tetras, raphaels, and a BN pleco, and they were (and are) fine. Colin, just out of curiosity, do you know or have any hypotheses for why a possible protozoan infection like this might infect only one species of fish in a community tank?

What is the base they are on is it silica sand.

Contamination is possible, I am always careful and the other fish seem fine though. Also it seems to kill them slowly one by one. I've been doing extra water changes just in case anyway.

I'll try and get a picture of the others today, I'll attempt a video but he was swimming normally again last time I checked.

itiwhetu said:

What is the base they are on is it silica sand.

Click to expand...

It's silver sand, not sure if that's different - this one https://www.swelluk.com/swell-aquarium-silver-sand/

Colin_T said:

Pictures of the other catfish?

Click to expand...

Here's a picture of 2 of the other fish that seem fine..

You know i had the exact same thing happen with Julii Cory’s I bought a month ago. Bought eight and one looked similar to the one in the pics with the red gills. I treated for gill flukes and they seemed to pick up after that. Not saying yours have the same but yours do have red gills and are spiraling towards the surface to get air and are breathing heavily. I used api general cure and it seemed to work plus I started vacuuming gravel twice a week. The ones you say are fine in the pics are showing inflamed gills which make me think gill flukes