Pencil fish illness

[Ben Rhau]

Hi all,

I've lost a handful of Nannostomus marginatus over the last year, all from what appears to be the same ailment. Usually the first symptom I see is droopiness or dark coloration in the body at the tail. The fish becomes more shy, and as the illness progresses, I start to see buoyancy control problems at the tail. For example, I will see the tail rise for a second, and then the fish will correct. If I let this persist, the fish will eventually lose buoyancy control, so the tail is elevated most of the time. Once the problem becomes this extreme, I put the fish down.

I haven't been able to find much information online to match these symptoms. Is anyone familiar with this illness and how to treat? Is it a bacterial infection, and is it contagious? I haven't tried medicating. I typically make sure the fish gets a lot of live BBS, and my water parameters are always pristine.

Any insight appreciated.

Thanks,
Ben

 

[MacZ]

How old are the fish? It sounds a bit like age related bacterial problems I have seen in other species. With bacterial infections waterchanges and alder cones are my go to.

 

[Ben Rhau]

It’s hard to say. Early part of last year I acquired 6 very large specimens (4 - 5 cm), so I assume those were mature. Of those, only one (the dominant one) remains. Around June, I acquired 8 of more typical size (about 3 cm). I had to transfer those to a different tank, and one of those 8 got sick. Guessing the stress made it hard to suppress an underlying condition.

All my tanks have alder cones and various leaf litter, and I do 30% weekly water changes.

 

[MacZ]

It could be a species-linked pathogen, then. If that's the case there is no med against that, only preventive measures. Basically you will have to get every specimen, in which it becomes acute, through it separately. But afterwards they are usually almost indestructable.

Up the waterchanges when a specimen has acute symptoms to 50% every other day. That way I just recently got a hard case of bacterial caused dropsy turned around.

 

[Ben Rhau]

Curious, if there is very low nitrate, what benefit do the water changes bring? Higher dissolved oxygen?

 

[MacZ]

Mostly lower pressure by pathogens and other wasteproducts than nitrates that we don't test for on the immune system. And gram-negative bacteria have a harder time multiplying.