Branchiomycosis (Gill Rot Disease)

o   Branchiomycosis is caused by two species, B. sanguinis and B. demingrans. They are currently in the Kingdom Chromista, a diverse group that includes diatoms, brown algae, and other water molds including Saprolegnia spp.

o   The species B. sanguinis and B. demingrans have been differentiated based on differences in hyphae and spore diameter and the location of hyphae within fish gills. The B. sanguinus species has hyphae that are 8-30 μm in diameter, and spores that are 5-9 μm in diameter, and it is found only in the blood vessels of the gills. The other species, B. demingrans, is found in gill tissues outside of blood vessels and its spores are larger in diameter (12-17 μm) (Goodwin, 2012).

o   Branchiomyces spp has been reported in a broad taxonomic range of fish species. Given this broad host range, it is likely that many more species of freshwater cultured fish only are susceptible to branchiomycosis (Goodwin, 2012).

o   Poor-quality water at the sites of infection (environmental stress including ammonia, nitrite and organic matter) could be a major predisposing cause of this fungal infection. As expected, water reuse systems (Closed systems) are more susceptible to its infection than other culture systems (El-sayed, 2020).

o   The fungus invades the gill via branchial vessels or the epithelium and can cause massive destruction of respiratory surfaces (El-Sayed, 2020). The invasive fungal hyphae obstruct the circulation of the blood through the gills. Outbreaks appear may be unpredictable although mortalities up to 50% have been recorded.