A case of Pseudotropheus demasoni inexplicable deaths

 By Antonis Roussos

Sometimes, things just happen, no matter how hard we try to avoid them. To be more specific, even a healthy aquarium may experience massive deaths for no apparent reason. I had the impression that my tank was in good condition. The water parameters were OK and one of my Labidochromis caeruleus sp. ‘yellow’ spawned. And then, the disaster began…

In my 160 litres M’buna tank, four Pseudotropheus demasoni, five Labidochromis caeruleus sp. ‘yellow’ and one Synodontis sp. were living happily until something strange happened. After a routine water change one of my P. demasoni began to face equilibrium disorder problems (swimming erratically), lying on the sand like dead while breathing normally but being unable to swim at all. After talking to some friends we came to the conclusion that it could be …anything: A bacterial infection, an internal parasite or both. The body of the fish didn’t seem harmed and the fish’s colours were great. That’s because the fish wanted to show to the other individuals of its species that it was still able to fight, even if it wasn’t. What a fighter!

My first action was to remove the Synodontis catfish since it could have fought with the P. demasoni hard enough to cause some internal damage to it, but I was wrong. After a few days, while the Synodontis was still away, a second P. demasoni showed the same problem, proving that the Synodontis was innocent. I quarantined the two sick guys and began to think of what I should do next. Since it could be a bacterial infection I should use a medication which would eradicate the pathogen once and for all. After some conversation with fellow hobbyists I decided to use Minocycline hydrochloride or Minocin (trademark in Greece), a strong medication for human purpose able to kill the bacteria with the additional advantage that it will get into the bloodstream of the fish through the gills. In order to be sure that all the fish would be healthy after the treatment of the two sick P. demasoni (despite the fact that the Labidochromis caeruleus were looking not infected and completely healthy) I treated the whole tank. I turned off the lights, I removed the activated carbon and the treatment started (for more info on how to use Minocin read the article: ‘Only you can save your fish’. After four days, on the day the treatment was supposed to come to an end, the third P. demasoni got sick too! It all happened a few moments after the vast water change of 50% that I made in order to remove the medication from the water.

It seemed that it was more than just a bacterial infection. Maybe a parasite was causing (or worsening) the problem and the bacterial infection was the consequence of this. So I had to treat the whole tank again with a medication able to kill the (possible?) parasite. This time I chose the General Cure by Aquarium Pharmaceuticals. This is an expensive medication that should be used in relatively small tanks so that the cost stays within normal limits. For instance, I needed a whole pack of 8 capsules to treat my 160 litres tank. Before adding it into the water I waited for four days doing 25% daily water changes in order to remove Minocin first.

This is how the pack of the General Cure product looks like.

When the treatment with General Cure was completed, I made the 50% water change in order to remove the parasite control cure and the worst happened… the fourth, larger and healthier P. demasoni got sick too and died the day after! After two treatments was there something still in my water or was it  only inside my P. demasoni’s organism?

Now, two of my initially four P. demasoni are still alive and swim again as happily as they used to, enjoying daily 10% water changes I make in order to remove the medication completely from the tank. I also use some activated carbon for this purpose. Fortunately, I managed to keep them alive but unfortunately I lost the other two... The mystery remains but at least I know that I‘ve done my best and the pathogen was probably in the fishes from the early beginning, before I added them in the tank. Maybe the exporter / importer of the P. demasoni didn’t care enough for their feeding and water parameters and the infection was ‘waiting’ for the right time to attack. Maybe I made a mistake no matter how hard I tried to avoid it. What matters most is that two P. demasoni are alive and the Labidochromis caeruleus are doing great since I first added them in my system. As soon as I know more about the cause for this “killer” pathogen which devastated by P. demasoni I will update this article.

Another thing that I realized after this incident is that quarantining a fish before adding it in your tank and treat it for parasites and bacteria is a wise thing to do. In my case, some of my fish, no matter their size or how healthy they looked, were probably too sick to be treated effectively anyway, but at least I would have avoided treating the whole tank. If I had used a smaller tank as a quarantine I would have treated them in it without risking my useful bacteria colony in the main tank. As a final remark, I can only tell you one thing: Don’t get disappointed if something goes wrong without any obvious reason. Try to face it and no matter the results, the experience will make you a better hobbyist.

This is one of my two survivors. The fish seems exhausted from all the treatment and it’s colours are dull but it swims and eats like a healthy one. I hope that it will be in great shape soon.

That’s the same fish with the male coloration ready to be shown no matter the two treatments. It may seem in perfect shape but an experienced fish keeper will notice that the colours could be brighter and sharper and the contrast much better.

Another shot of the little survivor. A few days ago it was lying on the sand but now it’s back in action.


Thanks to the MCH family for its support. Without it I couldn’t have saved even one of my P. demasoni. Too bad there are fish importers / exporters who only care for money and not for healthy fish and happy hobbyists.

 If anyone has already faced or faces a similar incident with the same symptoms please contact me via:

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