Hi. I am slowly losing all my Boseman rainbows to a mystery illness - two have developed dark lumps near their dorsal fins and the others have withered away and were breathing very rapidly. I’ve also now started losing my platys. They seem to just fold up their fins and begin to breathe fast. I can’t treat the whole tank with some medications as I have loaches but I do have a quarantine tank. Can anyone advise what may be causing this please? I can’t see any other lumps or spots. Photo of the rainbow attached.

Rainbowfish are highly susceptible to mycobacterium infection (fish TB). While this does sound like it, it could just be a bacterial infection which will clear up with Esha 2000. This is safe for all fish. If it doesn't clear up with treatment then mycobacteriosis is more likely but can only be confirmed with a skin scrape tested by a vet. Unfortunately, there is no cure for this and the usual recommendation Is to euthanise the fish and completely strip and disinfect the tank and its contents before starting again.

1. Identifying Symptoms and Possible Causes

The symptoms you describe in your Boseman rainbows and platys—dark lumps near the dorsal fins, rapid breathing, and fin folding—can be indicative of several underlying health issues. Here are some potential causes:

Infectious Diseases:

Bacterial Infections:
These can manifest as lumps or lesions on the body. Common bacterial infections include Columnaris (Flexibacter) and Aeromonas, which can cause skin lesions and respiratory distress.
Parasitic Infections:
External parasites like Ichthyophthirius multifiliis (Ich) or flukes can lead to stress, rapid gill movement, and overall poor health. Internal parasites may also cause similar symptoms but would typically require a different approach for diagnosis.

Environmental Factors:

Water Quality Issues:
Poor water quality is one of the most common causes of fish stress and illness. High levels of ammonia, nitrites, or nitrates can lead to respiratory problems. Testing your water parameters (pH, ammonia, nitrite, nitrate) is crucial.
Temperature Fluctuations:
Sudden changes in temperature can stress fish significantly. Ensure that your tank maintains a stable temperature suitable for both your rainbows and platys.
Nutritional Deficiencies:
A lack of essential nutrients can weaken fish immune systems, making them more susceptible to diseases.

2. Quarantine Tank Utilization

Since you have a quarantine tank available, it is advisable to use it for treating affected fish while minimizing the risk to your loaches in the main tank. Here’s how to proceed:

Isolate Affected Fish:
Move any visibly sick fish into the quarantine tank immediately to prevent further spread of disease.
Monitor Water Conditions:
Ensure that the quarantine tank has optimal water conditions similar to those in your main tank.

Treatment Options:
For suspected bacterial infections, consider using antibiotics such as erythromycin or tetracycline.
For parasitic infections, treatments like praziquantel (for flukes) or copper-based medications (for external parasites) might be appropriate.

3. Preventive Measures

To prevent future outbreaks:

Regularly test water parameters and perform routine maintenance such as partial water changes.
Ensure a balanced diet for all fish species in your aquarium.
Quarantine new arrivals before introducing them into the main tank.

4. Conclusion

Given the symptoms presented by both your Boseman rainbows and platys—particularly the presence of lumps and rapid breathing—it is likely that they are suffering from either an infectious disease or environmental stressors related to water quality. Immediate action through isolation in a quarantine tank followed by appropriate treatment based on observed symptoms will be critical in managing this situation effectively.

Thank you. Unfortunately, as I’m in the U.K., I can’t get hold of the antibiotics. I’ve had a look on eBay to buy from the US but they don’t seem to be available/are expensive/likely to be intercepted at the border. Do you have any other suggestions for treating the problem if it’s bacterial? Thanks.

As per my post above, Esha 2000 - available in many shops and online at Amazon.

Thank you. I’ve dosed the tank with flubendazole. Do you know whether this can be used in combination with ESHA 2000 or will I need to wait? If I need to wait, how long to wait/how much of a water change? Thanks

No they can't be used together. Give the Flubendazole 48 hours to work then do a 50% water change and add carbon to your filter for 24 hours to remove the rest of it before treating with Esha 2000. Don't forget to remove the carbon before staring the Esha 2000.

Great. Thank you so much for your help.

Somewhere like Maidenhead Aquatics may stock something that can help