Dwarf Pencilfish bloated/deformed?

[JBFUK]

Quick overview. Planted 125L tank with a good sized external filter (Fluval 307). Injected CO2. Reasonably lean dosing. Water params ~ 50/50 RO/Tapwater (hardwater); GH 12, KH 6,NH3 0, NO2 0, NO3 ~20ppm, PO4 ~0.5ppm. PH between 6.8-7.8 depending on time of day (changes with CO2 levels). Livestock - 8x Dwarf Pencilfish, 1x Pleco, 3x Corey (small), 2x guppys, 2x black pahntom tetras, 12x Lambchop Rasbora, 10x Chilli Rasbora, ~40 cherry shrimp, various snails. Sounds like quite a lot but the rasboras are all tiny so have very little bio-load.

Generally the tank seems quite healthy, I change 30-40L weekly, clean eheim pre-filter with water changes and the canister filter every 1-2 months.

I've noticed a few of my pencilfish have a bit of a bloated stomach. I'd presumed these were the females with some eggs. However, one in particular has become very bloated to the point that it looks deformed. I've also noticed that the female guppy looks pregnant even when she's given birth.

Having read a little about bloating I'm concerned that the fish in question may have something called dropsy?

I'm attaching a few photos, sorry if they aren't clear but the fish don't stay still for long! Does this sound like a sane diagnosis?

If this is the case, what's the best thing to do to treat them? Of course youtube is full of all sorts of conflicting information. I have a small 34L tank I could setup for quarantine/treatment if I have to. I've seen advice ranging from feeding vegetable matter only, API aquarium salt, API metafix, antibiotics, epsom salts etc. I wonder also whether I should only treat the fish that are clearly effected or also those suspected (the pencilfish with a slightly plump belly)?

 

[Byron]

The pencilfish in the photos (assume this is the same one) is in trouble, and I don't guess on disease but members like @Colin_T will have a better idea. Do not be quick to start dumping "medications" in, this fish is a characin and they have a sensitivity to chemicals in the water. Colin will best advise if something is needed. It may be genetic, as there is evidence of a spinal deformation.

 

[JBFUK]

Yes I do fear she/he’s in trouble and three of the others have less extreme but similar symptoms.

I noticed that when resting they seem to have a bit of a bend in the spine, to the right, when viewed from above.

The fact my female guppy has also for some time looked a bit bloated now concerns me. I’d thought she was pregnant but she recently had a batch of fry and still looked fully pregnant afterwards. I don’t see the standing up scales that I’ve seen in photos of fish with extreme dropsy but it sounds like one of the more likely culprits. As you say the pencilfish could also have some genetic problem or perhaps be egg bound?

Haven’t done anything yet, I’ll wait for some advice. I really like my pencil fish, they are probably my favourites so would be a real shame if I lose them.

 

[Byron]

I'm not suggesting this as "the" issue, just noting for information. Depending where you acquired the pencilfish, this species Nannostomus marginatus is probably wild caught. This species is a widespread polymorphic one, with distinct populations occurring in the Guyanas and in several widely-separated areas in the Amazon basin. At least three distinct colour variants are known. Their habitats all have very soft somewhat acidic water. Wild-caught fish are said not to last in basic or harder water. Diffused CO2 can cause issues for fish, again not saying it is here, but it is worth recognizing. Link to an article from PFK, there are other articles there too on CO2's damage to fish.

Does CO2 injection cause disease?

Does CO2 injection cause disease?

www.practicalfishkeeping.co.uk

 

[JBFUK]

Interesting, Tropco (where I brought them) lists them as Nannostromus Beckfordi, but calls them dwarf pencilfish - which you correctly described as Nannostomus marginatus.

It would be a shame if they are being affected by my water parameters. Running 50% RO is enough of a hassle, I wouldn’t want to use a higher ratio. Interesting read regards the CO2, I haven’t had any issues with other fish.

 

[Byron]

Interesting, Tropco (where I brought them) lists them as Nannostromus Beckfordi, but calls them dwarf pencilfish - which you correctly described as Nannostomus marginatus.

These are two distinct species, and N. beckfordi is being commercially raised and is rather less demanding, but compatibility-wise it is very feisty and can nip. But the photos above are without question N. marginatus. Over the past 30 years I have maintained ten species of Nannostomus, every time a species would turn up locally (all were wild caught).

 

[JBFUK]

Reading the stickys on this forum, I even wonder whether it could be internal worms. Could certainly explain the bloated guppy, I don't know about the pencilfish.