Congo Tetras Slowly Dying

[Coys]

I have, or rather had, eight Congo Tetras; I bought them all as young males about 3.5 years ago and until about three months ago all were fine, feeding well, swimming around as a shoal, occasionally fighting and looking healthy.

Then one by one they go through the same process; go off their food, lose colour, swim around slowly or lurk alone in a corner, mouth opening and closing more rapidly each day, until I have to euthanise them. Another one went this morning and I'm now down to three, although one of those is showing early symptoms and I suspect that he will go the same way in less than a week.

There are no external signs of illness apart from colour loss. Water conditions are good and all other fish (Bentosi, Rummynose and Silvertip Tetras) are fine.

Is this likely to be old age (3.5 years plus however old they were when I bought them) or something else?

 

[nel.pogorzelska]

Congo tetras live 3-5 years, so it's possible they are just getting old. Don't know how young they were when you got them, but assuming a few months, they might be reaching 4 years now. I've heard they can reach 6 years, but usually they'll live those 3-5, so it's definitely time for them

 

[Coys]

I suspected that may be the case.

 

[alto]

I'm not convinced - I've seen old Congo Tetras
and, well, they begin to look old just like other fish that begin to fail through aging

Disclaimer: not my fish but were in a large planted display tank at local shop

OTOH symptoms such as this tend to indicate some internal virus or latent bacteria so unlikely to be treatable
As you can predict the end now, I'd just euthanize once fish seems more stressed than OK

I'd not introduce any more Congo Tetras into this tank

 

[sciencefiction]

I am inclined to agree with Alto.Diseases are often species related and manifest by entire group of fish dying where all the rest of the fish seem fine. It is unlikely all fish die almost at once of old age, some always outlive the others by a big margin.
It is impossible to say what it is, but considering you're giving a time frame of 3 months, I'd suspect parasites/worms rather than bacteria/virus.It is possible, because of the tetra's old age, they're the first affected but it is not to say the rest aren't infected with the same. Healthy fish can often deal with parasites/worms without any visible signs. You mentioned that they're gasping, so it could be something affecting their gills, which could be as simple as flukes.

 

[alto]

Gill flukes would be fairly obvious especially on such a relatively large (tetra) fish

I'll disagree on the unlikelood of viruses (think iridovirus) & bacteria (think mycobacterium sp)

I find parasites,worms to respond well to treatment even when started relatively late in the disease process (assuming you've access to actual fish effective meds)

 

[Tim Harrison]

I'd give them a broad spectrum treatment. Combine eSHa 2000, EXIT, and gdex, it's combination that will cover most diseases and it's usually well tolerated.

 

[sciencefiction]

I find parasites,worms to respond well to treatment even when started relatively late in the disease process (assuming you've access to actual fish effective meds)

Yes, fish will respond if treated with correct meds.
I though bacteria at first because bacterial diseases are species related but the time frame is too long. Mycobacteria is possible, then again they wouldn't all die at the same time, plus it will manifest in more fish, more odd symptoms, not just loss of colour and gasping..With myco it is more likely they die over a way longer period, rather than in 3 months one after the other...plus of course all fish would be pretty much infected.

Virus, I don't know, it's got to be one specific to these tetras?

I am suggesting parasites/worms because it is so common in fish, and are the triggers for more serious issues. In good water conditions one might not notice for months until something triggers it off and some fish start dying. The stress trigger could be water quality, tank re-arrangement, new tank mates, noise, anything really that can affect the well being and immune system of fish.

 

[Coys]

I did treat a probable columnaris outbreak on a new batch of silvertips in March, but I'm sure that came with the new fish and no other fish were affected by it; the Congo die-off had already begun by then. Four of the Silvertips died rapidly despite the treatment, but the other six are thriving. None of the other established fish (primarily Rummynose and Bentosi) were affected by the columnaris. It's definitely not gill flukes and the Congos do not appear to lose weight either.

 

[alto]

Mycobacteria is possible, then again they wouldn't all die at the same time, plus it will manifest in more fish, more odd symptoms, not just loss of colour and gasping..With myco it is more likely they die over a way longer period, rather than in 3 months one after the other...plus of course all fish would be pretty much infected.

What OP is seeing is consistent with my observations with anabantoid sp infected with mycobacterium, including Sphaherichthys - note this does not seem to infect all species within tank (providing fish are nonstressed).
Some sp of mycobacterium more infectious than others
(no necropsy but based upon educated guess: consistent symptoms (complete lack of response to all attempts at isolation & medications), high incidence found in juvenile & breeding stock at farms etc)

There are also many other less well known internal pathogens

 

[alto]

Virus, I don't know, it's got to be one specific to these tetras?

No, some species react differently or have varying susceptibilities

 

[sciencefiction]

but the other six are thriving.

They're ca

What OP is seeing is consistent with my observations with anabantoid sp infected with mycobacterium, including Sphaherichthys - note this does not seem to infect all species within tank (providing fish are nonstressed).
Some sp of mycobacterium more infectious than others
(no necropsy but based upon educated guess: consistent symptoms (complete lack of response to all attempts at isolation & medications), high incidence found in juvenile & breeding stock at farms etc)

There are also many other less well known internal pathogens

Yes, I am aware of that but myco has been thrown at people all the time for anything unexplained....

 

[alto]

Because incidence rate may range from 40-70%, one farm had nearly 90% in breeding stock, fry showed up to 40% & this observed infection rate likely increased as they grew out (surmise by authors)

 

[sciencefiction]

I did treat a probable columnaris outbreak on a new batch of silvertips in March, but I'm sure that came with the new fish and no other fish were affected by it; the Congo die-off had already begun by then. Four of the Silvertips died rapidly despite the treatment, but the other six are thriving. None of the other established fish (primarily Rummynose and Bentosi) were affected by the columnaris. It's definitely not gill flukes and the Congos do not appear to lose weight either.

You don't need columnaris to be introduced. Also, some fish are life time carriers of columnaris. I had harlequin rasboras infected with columnaris last year.
Loss of colour and gasping were the signs, only one showed the typical saddleback and mouth eriosion. The others died too fast. Majority survived as I treated with antibiotic the moment I noticed. Mine were dropping in the space of a week though.

Also, to add to the above, the 2 clown loaches quarantined with the same rasboras did not show any signs of the disease at all.

 

[alto]

Iridovirus levels also hit 40% in suspectible species, with observed incidence possibly increasing with age (again surmised)

 

[sciencefiction]

And % infected with worms and parasites? I'd guess way above...

 

[sciencefiction]

I have to dig out the nice paper I read on columnaris, but fish infected with parasites/worms are way more susceptible of dying of columnaris once infected, than those that don't carry parasites/worms. That's why its in the best interest of everyone to de-worm their new fish with appropriate meds.

 

[Coys]

You don't need columnaris to be introduced.

I'm 100% sure that I saw the beginnings on coumnaris on two of the silvertips within 24 hours of them arriving, so in this case it did come with them. Can't say I'm happy with the supplier. As suggested I'll treat with eSHa 2000, EXIT and gdex and see how things go before risking introducing any new fish.

 

[sciencefiction]

I'm 100% sure that I saw the beginnings on coumnaris on two of the silvertips within 24 hours of them arriving, so in this case it did come with them. Can't say I'm happy with the supplier. As suggested I'll treat with eSHa 2000, EXIT and gdex and see how things go before risking introducing any new fish.

Same happened to me. They were new fish and my first columnaris case. However, when your own tanks holds carriers of the disease which are visually unaffected, it is new fish that will show the symptoms once they're in contact with a bacteria they're not immune to. This is the case with wild fish introduced to the confinements of fish tanks and subjected to a range of micro-organisms that they had never encountered before. It is all dependent on the immune system of fish who lives and who dies. Fish tanks are full of pathogenic organisms. All we do is provide an excellent environment for the fish, the immune system deals with the rest. Compromise the immune system and fish can show symptoms of disease. So it is very difficult to tell where the disease came from...

 

[sciencefiction]

Fish may reside in a clinically healthy carrier status harbouring an isolate remaining from a previous outbreak of columnaris disease and in this way act as an infection source for other fish

The gills were shown to be the major release site of this pathogen.

The bacterium can keep its infectivity in lake water in laboratory conditions for at least five months

Besides the virulence of the strain being a determinant factor, in coldwater and temperate fish, age also seems to have an important impact on the severity of the clinical signs. In young fish, the disease develops acutely and mostly damages the gills (Figure 1). In adults, the disease may adopt an acute, subacute or chronic course. When the disease course is acute or subacute in adult fish, yellowish areas of necrotic tissue can appear in the gills ultimately resulting in complete gill destruction

In chronic cases, it takes longer before gill damage appears and skin lesions may develop as well.

Quoted from below:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3648355/