A Chytrid fungus is a very primitive form of fungus that belongs to the Chytridiomycota fungal family. There are over 1000 known Chytrid fungal species that are subdivided into 127 genera and classified into five orders. Most of these Chytridiales are generally found in aquatic or moist environments, since, being of the zoosporic fungi type, it is necessary for these fungi to have a watery medium in which to transmit their spores. The fungi may be free-living saprobes, that is, fungi that subside on dead and decaying organic waste, or they may be parasites dependent on live plants and live invertebrates.

The cell wall of the chytrid fungus is made of chitin, and some species maybe multicellular or unicellular. As mentioned, the chytrid fungus propagates by means of zoospores. Each spore is mobile and has a single flagellum that helps it to navigate its way through water. These zoospores are only capable of existing and thriving in a cool, watery environment; they cannot survive for very long in dry, warm conditions.

One of the most well-known of the Chytrid fungus is the species called Batrachochytrium dendrobatidis. This fungus causes chytridiomycosisis, a deadly fungal disease that has been responsible for wiping out entire populations of frogs and other amphibians in many parts of the world. According to researchers, the fungus consumes the keratin in the skin of the infected animal and causes the amphibian skin to thicken. This skin thickening prevents normal respiration through the skin, and leads to a build up of potassium and sodium electrolyte salts. An overabundance of these electrolyte salts leads to heart failure.

Some infected amphibians die at once, while others may be ill for a while before succumbing. Death is certain if the disease is not treated, and treatments may not always work. There have been some successes using benzalkonium chloride, copper sulfate, formalin, malachite green and terbinafine hydrochloride.

While it is possible for pet owners to treat their infected amphibians, treating, eradicating or preventing the chytridiomycosisis fungal disease in the wild amphibian populations is practically impossible. Since this is a highly transmittable disease, it is essential to restrict and regulate the transportation of amphibians from one country to another. All transported amphibians need to be tested prior to transport for the chytrid fungus, and it is equally necessary to observe strict quarantine rules in the new location. Frogs and amphibians used in laboratories should not be released into the wild, and if there are any infected creatures, they need to be isolated immediately.