Faunamor for Lionfish: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Faunamor is an immersion medication for ornamental finfish. In the U.S., it is FDA-indexed for ornamental finfish and contains three active ingredients: methylthionine chloride (methylene blue) 2.5 mg/mL, malachite green oxalate 1 mg/mL, and acriflavine chloride 0.3 mg/mL. It is sold as a dark blue liquid that is added to the aquarium water rather than given by mouth.

For lionfish, this matters because treatment is aimed at the water and the parasite load in the system, not only the individual fish. The product label says the entire aquarium should be treated, ultraviolet sterilizers should be turned off during treatment, and the dose should be based on the actual water volume in the tank.

Faunamor is labeled for ornamental finfish only. It is not for food fish, and it may be unsuitable for invertebrates such as shrimp, snails, mussels, and corals. If your lionfish is in a reef or mixed marine system, your vet can help you decide whether a hospital setup, another medication, or a different parasite-control plan is safer.

Faunamor is labeled for the treatment of Ichthyophthirius multifiliis, commonly called white spot disease or freshwater ich, along with associated bacterial infections in ornamental finfish. In fish medicine references, white spot disease can cause visible white dots on the skin, fins, or gills, rubbing or flashing, clamped fins, lethargy, and sometimes sudden losses when the gills are heavily affected.

That label indication is important for lionfish because most pet lionfish are marine fish, and the classic marine look-alike is Cryptocaryon irritans rather than freshwater ich. The FDA summary notes that malachite green and acriflavine have activity reported in the literature against a range of protozoal and external pathogens, but Faunamor's U.S. label is still specifically tied to ornamental finfish white spot disease and associated bacterial infections. Your vet can help confirm whether the problem is marine ich, velvet, bacterial skin disease, trauma, or another condition before treatment starts.

In practical terms, pet parents and aquarium professionals most often consider products in this class when a fish has external parasite signs and the whole system may be contaminated. Because lionfish can be sensitive, venomous to handle, and often live in marine systems with delicate tankmates, diagnosis and treatment planning with your vet is especially worthwhile.

Follow your vet's instructions first. The current U.S. Faunamor label gives a whole-aquarium immersion dose of 1 mL per 100 liters of aquarium water for three doses on Day 1, Day 2, and Day 7. The package insert also expresses this as 8 drops (0.4 mL) per 10 gallons on Day 1 and Day 2, then repeating the Day 1 treatment on Day 7. On Day 8, the label directs a 30% water change and restarting normal filtration.

The label also says that in severe cases, the dose may be doubled if there are no extremely delicate fish in the aquarium. It specifically warns that delicate fish, including catfish, may not tolerate higher dosing well. For lionfish, do not assume a severe-case dose is appropriate. Marine species, stressed fish, fish with gill disease, and fish in low-oxygen systems may need a more cautious plan from your vet.

Before dosing, remove or bypass filtration media as directed on the label, keep the biological media alive in separate aquarium water if needed, and provide strong oxygenation. Turn off UV sterilizers during treatment. Dose based on the real water volume after rock, sand, and décor displacement, not the tank's advertised size. Because this medication can affect tank chemistry, stain equipment, and be unsafe for many invertebrates, pet parents should review the full setup with their vet before treating a lionfish display tank.

The product label and fish medicine references suggest that dye-based medications in this class can be stressful to some fish and to the aquarium environment. Watch your lionfish closely for faster breathing, hanging near flow, loss of balance, worsening lethargy, reduced appetite, color change, or sudden distress after dosing. If signs worsen, contact your vet right away.

Faunamor turns the water blue, and staining of plastic, silicone, décor, and equipment can happen. The label also warns that it may be unsuitable for invertebrates, so shrimp, snails, mussels, corals, and similar animals should be removed before treatment. In mixed systems, this is often the biggest practical side effect because the medication may not be compatible with the rest of the tank.

The individual ingredients also carry important cautions. Fish references note that malachite green can be more toxic at higher temperatures and lower pH, and methylene blue may affect nitrifying bacteria and plants. That means some side effects are not only about the lionfish itself. They can also show up as reduced biofiltration, lower water quality, or oxygen stress if the system is not managed carefully during treatment.

Formal interaction studies for Faunamor in lionfish are limited, so the safest approach is to let your vet review everything in the system before combining treatments. That includes copper, formalin-based products, antibiotics, dips, water conditioners, salt or salinity changes, and any recent parasite medications. In fish medicine, stacking therapies can increase stress even when each product is reasonable on its own.

The package insert gives several practical compatibility warnings. UV sterilizers must be turned off during treatment, and filtration media may need to be removed or bypassed temporarily. Because methylene blue and related dyes can affect the tank's biological balance, your vet may want to avoid combining Faunamor with other treatments that also stress biofiltration or oxygen levels.

If your lionfish lives in a reef or predator system, ask your vet whether a hospital tank, staged treatment plan, or alternative antiparasitic would be safer than combining multiple in-tank medications. This is especially important if the fish is already weak, breathing hard, or sharing water with invertebrates.