Sudden illness and death of synodontis catfish
 

I have a 40 gallon tank that had four fish in it. Two Asian Carp and two Synodontis Cats.
The fish are large and have been in the tank for at least 12 years. One of the carp developed a lump on its lower jaw that I thought was a fungus and began treating it as though it was fungus. I was using a fungus cure that has the active ingredients
Victoria Green and Acriflavine which turn the water green. The treatment instructions
were to take the activated charcoal out of the filters and add the medicine to the water.
After 48 hours add another dose of the same amount for another 48 hours. I did that 3 weeks ago and I am still observing the carp to see if the fungus is cured. What I am really writing about is what happened to one of my Synodontis Cats, a female. My other Synodontis Cat is male. Both were apparently healthy. Coincidentally with starting the fungus treatment I noticed that the belly of the female Synodontis had begun to swell,
swelling rather abruptly. At first I thought that she might be gravid with eggs but now I don't think that was it. The swelling increased rapidly and the fish became listless. After about 2 days she settled to the bottom of the tank and barely moved. On the forth day she was obviously dead. When I took her out of the tank her belly seemed to be filled with fluid. I didn't cut her open to see what was inside. Frankly, I didn't want to see it, whatever it was. I don't think that the fungus treatment had anything to do with the death of the Synodontis. The timing was coincidental.
I am asking what the illness could have been. It apparently came on suddenly and killed the fish in 4 days. That happened 3 weeks ago. The surviving male Synodontis seems fine. He's lonely because the male and female were a pair for over 12 years.

Has anyone seen or heard of anything like this. If so please let me know about it.

Thanks, Bonneidee

I know it has been a while since this was posted, but from the research i have done, (victoria)malachite green can be considered toxic to catfish and other small scale, or scaleless fish.

Thanks Pennpets. It is still a mystery to me. There was another large synodontis in the tank and he is still alive and seems healthy. I have since gotten rid of the large Asian carp and I have decided to stock up with several varieties of synodontis cats. I hope that the different species of synodontis don't grow up and start fighting all of the time.
The new ones are quite small now and don't fight. They seem mostly interested in food.

Bonneidee

The female who died may have had an underlying illness. I am sorry for your loss.
Keep in mind that many scaless fish (catfish as well) are not tolerant to many of the chemicals found in medications, especially copper.
Good luck with your newest fish.