Methylene blue is a widely used compound in aquaculture due to its antifungal, antiparasitic and disinfectant properties. It is mainly used to protect fish eggs from fungal growth and to treat various diseases in freshwater and saltwater fish. In addition, it is useful in counteracting the toxicity of ammonia and nitrites in aquariums.
In this article, we will explore the benefits of methylene blue in aquaculture, how and when to use it, as well as the precautions necessary for its safe application.
When to use methylene blue in fish?
Methylene blue is an effective treatment for a variety of conditions affecting aquarium fish, including:
- Superficial fungal infections : Used as an alternative to malachite green in sensitive fish.
- Preventing diseases in eggs and fry : Protects eggs from fungal growth.
- External parasites : Combats protozoa such as Costia, Chilodonella and Ichthyophthirius (Ich).
- Skin and gill diseases : Treats bacterial and parasitic infections.
- Ammonia and Nitrate Toxicity : Helps neutralize the effects of contaminated water.
- Stress in fish : Works as a prophylactic support to relieve stress during changes in the aquarium.
Methylene blue is safe for crustaceans such as crabs, shrimp, and snails if introduced slowly. However, it can damage live plants if exposed for a long time.
Uses of methylene blue in aquaculture
1. Preventing fungus in fish eggs
One of the most common uses of methylene blue is to prevent the growth of fungi and bacteria on fish eggs. The proliferation of these microorganisms can cause egg loss, affecting reproduction. This compound acts as a disinfectant and improves hatching rates.
2. Treatment of nitrate poisoning
Excessive nitrates in the water can cause "brown blood disease," a condition in which fish develop brown gills, constant panting, and lethargy. Methylene blue helps reverse this condition by reducing methemoglobin levels in the fish's blood.
3. Control of ammonia poisoning
Ammonia is highly toxic to fish and can build up due to decaying organic matter or untreated tap water. Symptoms include purple or red gills, lethargic behavior, and crimson stripes on the body. Methylene blue can neutralize the toxicity and improve aquarium health.
4. Velvet treatment (Oodinium)
Velvet disease, also called "gold dust," is a disease caused by parasites that affect freshwater and saltwater fish. Symptoms include a yellowish coating on the skin, rapid breathing, and lethargy. A small dose of methylene blue can eliminate these parasites and improve the health of the fish.
5. Reducing stress in fish
Fish can experience stress due to changes in the tank, transfers, or water disturbances. A preventative dose of methylene blue can help reduce anxiety and improve their overall well-being.
6. Treatment of Ichthyophthirius Multifiliis (Ich or white spot)
Ich is a common parasitic disease in aquariums, manifesting as small white spots on the skin of fish, irritation and lethargy. Methylene blue can reduce the spread of the parasite, although its combination with formaldehyde and malachite green is often more effective.
7. Correction of swim bladder disorders
This condition affects the fish's ability to float or balance. It can be caused by disease, digestive problems, or physical defects. Methylene blue helps reduce inflammation and improve mobility in affected fish.
How to use methylene blue in fish?
These are some general guidelines, it is recommended to consult a professional before use.
1. General treatment in aquariums (direct use in water)
✅ Recommended dosage:
- 1 ml of 1% methylene blue for every 10 liters of aquarium water .
- In large aquariums, use 10 ml per 100 liters of water .
✅ Procedure:
- Dilute the dose in a glass of aquarium water before adding it to the tank.
- Turn off the activated carbon filter , as it can absorb the medication.
- Continue treatment for 3 to 5 days , observing the behavior of the fish.
- Perform a 25-30% water change after treatment to remove any remaining medication.
📌 Important: Avoid overdosing, as it can affect the beneficial bacteria in the aquarium.
2. Preventing fungus in fish eggs
✅ Recommended dosage:
- 1-2 ml of 1% methylene blue per 10 liters of water in the incubator.
✅ Procedure:
- Add methylene blue to the incubation water after eggs are laid.
- Maintain the dose until hatching.
- Gradually reduce concentration with partial water changes once fry are free swimming.
📌 Recommendation: Do not use high doses, as they may affect the hatching of eggs.
3. Therapeutic bath for sick fish (intensive treatment)
✅ Recommended dosage:
- 5 ml of 1% methylene blue per liter of water in a separate container.
✅ Procedure:
- Fill a non-metallic container with aquarium water.
- Dissolve methylene blue in the indicated proportion.
- Immerse the fish in the solution for 5 to 10 minutes (do not exceed the recommended time).
- Reintroduce the fish into its main aquarium.
- If necessary, repeat the procedure once a day for 3 to 5 days .
📌 Caution: If the fish shows signs of extreme stress, reduce the exposure time.
4. Treatment of ammonia or nitrite poisoning
✅ Recommended dosage:
- 1-2 ml of 1% methylene blue per 10 liters of water in the aquarium.
✅ Procedure:
- Dilute the dose in a glass of aquarium water before adding it to the tank.
- Ensure good aeration in the aquarium.
- Maintain the dose for 3 days , monitoring the recovery of the fish.
- Perform a partial water change after treatment.
📌 Tip: Identify the cause of the problem to avoid future poisoning.
Precautions when using methylene blue in fish
Methylene blue is an effective treatment, but should be used with caution to avoid adverse effects:
✅ Avoid overdosing : It can negatively affect the health of fish and beneficial microorganisms in the aquarium.
✅ Do not combine with erythromycin or tetracycline : The interaction with these antibiotics can alter the chemical balance of the water.
✅ Remove the activated carbon filter : To prevent the filter from removing the medication from the water before it takes effect.
✅ Monitor the aquarium after treatment : Replace 25% of the water after 3 to 5 days and reinstall the activated carbon filter.
✅ Avoid contact with live plants : This can damage them if exposed for a long time.
Frequently Asked Questions
Is methylene blue safe for fish?
Yes, it is safe if used in proper doses and not overdosed.
Can methylene blue harm aquarium plants?
If used in high concentrations or for prolonged periods, it can affect living plants.
Does methylene blue kill fish lice?
Yes, it is effective against external parasites, including fish lice.
Can you cure fin rot?
Yes, due to its antifungal and antiparasitic properties, it can help in the treatment of fin rot.
Can methylene blue be used on saltwater fish?
Yes, but it is recommended to adjust the dosage and use it in a quarantine tank when possible.
Methylene blue is a valuable ally in aquaculture when used correctly. Its ability to treat diseases, reduce stress and protect fish eggs makes it an essential product for any aquarist. However, it is essential to follow the recommended dosages and take the necessary precautions to avoid negative effects on the aquarium ecosystem.
