Virulent Disease, Need Help :(

Tank
What is the water volume of the tank? 55 Gallons
How long has the tank been running? 5 Months
Does it have a filter? Fluval 407 Canister + Aquaclear 50
Does it have a heater? Yes
What is the water temperature? 77 Degrees F
What is the entire stocking of this tank? 2 Rabbit snails + 4 rabbit snail babies, 2 trapdoor snails, lots of pest snails, 7 Blue-Eyed Signifiers (Pseudomugil Signifer), 4 Thicklipped Gouramis, 4 Synodontis Petricola

Maintenance
How often do you change the water? Once per week
How much of the water do you change? 30% to 50%
What do you use to treat your water? Seachem Prime
Do you vacuum the substrate or just the water? Just the water and I stir up the sand sometimes, but I rely on the malaysian trumpet snails to stir up the substrate

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes
What do you use to test the water? Aquarium Co-Op Test Stripes AND API Freshwater Master Test Kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: 0ppm
Nitrite: 0 ppm
Nitrate: 10 to 20 ppm
pH: 8.0

Feeding
How often do you feed your fish? Once per day
How much do you feed your fish? Some pellets to the gouramis, crushed flakes for the pseudomugils, sinking pellets or gel food for the snails/catfish
What brand of food do you feed your fish? A mix. Repashy, Omega One, Fluval, Xtreme Aquatics
Do you feed frozen? Twice a week, Daphnia
Do you feed freeze-dried foods? No

Illness & Symptoms
How long have you had this fish? 4 Months
How long ago did you first notice these symptoms? 2 Months ago
In a few words, can you explain the symptoms? My pseudomugil signifers have been giving me so much trouble and I'm really tired and at my wit's end. They were the first fish to go into the tank. I had them in the tank by themselves for two full months, treated them with several rounds of prazipro/general cure AND fed them a course of Kanaplex-in-Fish-Food for 10 days to try and clear some white lip. They seemed okay after that, and I had read that plenty of clean water changes can help de-stress these fish and get them settled. They were active, showing off around the tank, etc. There was always one weaker than the rest, skinnier than the rest, with very pale coloration. I thought initially he was subdominant, because though weak at first, he seemed to recover. Then, two months in, he got weaker, and weaker, and weaker, and wasted away. I separated him and attempted to treat with Levamisole, but it was too late, and I found him corkscrewing listlessly around the tank. I ended up euthanizing.

Since then it's been a nightmare. I've tried levamisole and noticed no improvement, second round administered last night. Haven't seen real evidence of worms. Another fish was pale and weak so I removed and euthanized. Now I am noticing one of my pseudomugils has a bloody lesion/redness around one side, near the gill plate. He had a stringy white poop today, too, and is SLIGHTLY paler than the others, though still active and eating.

Have you started any treatment for the illness? I tried general cure first. Then I did Levamisole, two rounds, along with Metronidazole in food. Now I'm fully despairing about the rest of my tank and I have grown very tired and upset with my pseudomugils.

Was your fish physically ill or injured upon purchase? One was visibly weak. Fins were frayed.

How has its behavior and appearance changed, if at all? No change in behavior of the remaining fish, but one is still visibly discolored.

Explain your emergency situation in detail.

I tried to explain in-depth above what is happening. I want to emphasize that the only fish displaying symptoms of any kind are my pseudomugil signifers, and it's happening one-by-one. I suspect I'll need to bomb the tank with heavy antibiotics but I'm scared of stressing and hurting my healthy fish, and I don't know if it will do more harm than good to them. Should I pull all the rainbows from the tank and treat them separately? Should I treat the entire 55 gallon? what should I use, if so? I included some images of the fish who is starting to deteriorate, but it's hard to see it in the photos -- he just looks slightly less colored and slightly pink in the gill area (it's more intense in person). Please help. I really tried to do this right and quarantine ALL new additions appropriately, and it doesn't seem to have helped me out this time.

Thank you.

 

I've never kept those fish before so you can take this with a grain of salt but maybe it's wasting disease/ normal pecking order weakness? As in when the lowest fish dies a different one takes the brunt of the aggression which weakens it and opens it up to the disease. Honestly that's the only thing I can think of that would only target one fish and not be treatable.

 

pufferpresence20 It's a pretty reasonable idea and one I considered. Pseudomugil signifer males are extremely intense to bottom-rungers, and I've heard that in confined conditions (too-small tanks and too-few-in-the-school), males will sometimes kill the weakest. They do spar regularly and seem vigorous enough, except one will start to lose color and waste slowly away.

I decided since nematodes were the missing link for showing up two months after I brought them home and put them through a solid quarantine period, Levamisole would be my last resort. But now I'm seeing probable secondary bacterial infections. At this stage, I have resigned myself to believing that these fish are sensitive and/or weak stock, since virtually none of my other fish have shown signs of problems. But I really want to keep it that way, you know? My thicklips in that tank are my favorite fish in my fish room, and I'd be devastated if they caught something from these guys. I had thought after two months of quarantine they didn't have anything contagious, but, well, here I am.

I do have tons of meds that I can use, but I'm not sure where to proceed from here, or what would be the smartest choice that will cause the least harm to my healthy fish. I had another experienced person recommend trying oxytetracycline in food alongside the levamisole treatment since the group already went through a kanaplex-in-food treatment. If that's safe enough, I can start that course as soon as tomorrow.

 

I can't really speak to whether or not the oxytetracycline would work, honestly you sound like you know more about it, but in terms of keeping the other fish healthy I would probably quarantine and decide from there what to do with the sick ones. I don't think you probably need to treat the entire tank since you said everyone else is healthy, although if you go with a less stressful medication it might be worth it just to be safe.

 

I'm going to update what happened and how it's going. I went from 10 pseudomugil signifers all the way down to 5 left. The latest death happened today.

The tank has been treated with antibiotics in food (oxytetracycline AND kanamycin), levamisole, metronidazole in food, and praziquantel -- all spaced appropriately apart. I ceased all treatments in late December. Pseudomugils continued to waste and die until then, and I was left with 6. All seemed well between the end of December and now.

Today, abruptly, another pseudomugil started drifting and cartwheeling listlessly around the tank, clearly on his way out. He was eating just fine this morning and yesterday. I took him out and euthanized with clove oil as he wasn't going to make it back from that. Five left.

I can't say I would recommend this fish unless you know your source and the age of the fish well. I don't think this is a contagious disease as it affects the pseudomugils and only the pseudomugils; my gouramis and synodontis catfish are both vigorous and well.