Fish Seem Contagious, Help ID Culprit

[SeemsFishy]

I've lost 4 danios over the course of the past week and I'm worried at least 1 more may go down this path. The 20g tank only has danios and a dwarf frog.

A - 0
NA - 0
Ni - 20
Added new driftwood about 5 weeks ago, tied existing plants around it and all seemed fine.
Weekly 30% wc with gravel vac due to messy adf

It began with Mean Mean Fishy Face, the tank bully lady, who was big like before laying eggs. After her stomach deflated from the eggs, she had this odd sail shaped mass in her stomach. I thought maybe she was a bit fat and overfed.

She stayed with the notch for weeks, still ate, no other apparent problem. Then she started hanging out towards the bottom more often and other fish took over her usual territories. After a couple days of not eating and hanging out in the bottom half more, another danio started hanging out at the bottom. I qt'd both to a hospital tank filled with tank water and dosed with kanaplex.

The second fish to fall ill died overnight with no other sign or warning. Mean Mean seemed to be doing well. Her stomach flattened out, still no eating. After another day of looking better, Mean Mean died and had a large bruise under her skin only on one side (yellow fish photo) right after.

Fyi, I did daily 50% WC in hospital tank adding tank water and redosed kplex for added water only. Temp and other parameters matched between the tanks. I tested a/n/n twice daily to confirm all was well.

After that, 2 more fish in the main tank got sick. Both males developed the same sail shaped notch on their stomachs (pink fish photo) and started laying on the bottom. This was more sudden than the others.

I sanitized the hospital tank, tried again with both of them on kanaplex. After 48 hours of looking better, and the notch smoothing out, they started laying on the ground in a c shape. They'd occasionally try to swim but would have no successful direction and would lay in a c shape on the ground. They died quickly within an hour of this behavior (before I could figure out if they could be saved or should be euthanized).

Now, my last female in the main tank is swoll up like she's with eggs for a few days now (no pineconing or dropsy look), but she's not eating, towards the bottom, and I worry her eggs may be hiding that sail shaped notch. There are 3 other danios in the tank seemingly normal, ironically the weakest fish between physical deformities from birth or being juveniles, and an adf.

I can't tell what this is, how to save them, if the others are done for, how to clean/save this tank, and ultimately how to treat them all. Thouhts please?

 

[fearlessfisch]

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Sunken belly is often a sign of internal parasites. Do you also see white or stringy poop?



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Your nitrItes were zero and nitrAtes were 20, right? Just checking because you wrote Ni is 20.

 

[fearlessfisch]

Also, generally you should use at least 50 percent clean water to start, in a quarantine tank, rather than all tank water. From then on, do water changes with clean water only. Unless you have not been doing regular water changes for a long time (in which case your fish could be shocked by clean water), your fish will generally appreciate and benefit from the cleaner water. I actually tend to do a large water change in the main tank before moving a fish to quarantine, and just use clean water in the QT tank. In general, sick fish benefit from as much clean, fresh water as possible.

If your fish have internal parasites, it is especially important to be changing water in both the main tank and the QT tank, so as to remove nasties from the water.

As always, match temperature and don't skip the dechlorinator.

 

[SeemsFishy]

Thank you. Correct on the numbers mix up, and I do the water changes weekly like clockwork so no problems shocking the fish. And no stringy poop, none of them ever had it. Also no other external signs of parasites on the fish, in gravel, or free swimming.

I did a deep vacuuming of the gravel, removed the organic decorations, 75% wc, and cleaned any pieces of the tank except the bio filter. Next day I did another thorough gravel vac, 50% wc. Fish seem to be doing well and the four remaining are eating and swimming fine, though the big one does hav a bit of a sunken stomach.

I'll use general cure for parasites right away unless you think something more specific would work better.

Thanks again for the responses