Methylene Blue: Uses for Fungus, Eggs and Nitrite Poisoning
Methylene blue is a classic aquarium remedy used against fungus and external protozoa, to protect fish eggs, and as support for nitrite poisoning by restoring the blood's oxygen-carrying ability. Learn its evidence-based uses and why it is kept to bath or hospital use.
What methylene blue is used for
- Fungal infections, and especially protecting newly laid fish eggs from fungus during artificial hatching.
- External protozoa including Ichthyophthirius (ich), though other treatments are more effective for ich.
- Support for nitrite poisoning and methemoglobinemia.
How it helps with nitrite poisoning
Nitrite oxidizes hemoglobin to methemoglobin, which cannot carry oxygen. Methylene blue is a classical antidote for methemoglobinemia: it reduces methemoglobin back to functional hemoglobin, restoring oxygen transport. In a controlled study, Nile tilapia given methylene blue before nitrite exposure had no mortality while untreated controls died, and their gills were better preserved.
How it is used
Methylene blue is typically given as a medicated bath or dip rather than dosed into a main display, and it is used to treat eggs during hatching. Because it is a strong dye, it stains water and surfaces blue, so it is commonly confined to bare hospital or bath containers. Follow product instructions for concentration and duration.
Sources: Wikipedia, Methylene blue (CC BY-SA 4.0) (en.wikipedia.org); PubMed, methylene blue mitigates acute nitrite intoxication in Nile tilapia (pubmed.ncbi.nlm.nih.gov).