Branchiomycosis (Gill Rot) - Fungal Diseases of Fish

Branchiomycosis (Gill Rot)

CAUSATIVE AGENTS:

Branchiomyces spp.

SPECIES AFFECTED:

Carps, goldfish, eels

GROSS SIGNS:

Gills become pale with brownish areas due to hemorrhage and thrombosis, or grayish as a result of ischemia. Necrotic areas might slough-off at a later stage becoming a focus for saprolegnian infections.

EFFECTS ON HOSTS:

Fungal hyphae in the gills obstruct the circulation of the blood. Necrosis and proliferation of lamellar epithelial cells and lamellar fusions may be observed. The disease can appear suddenly and often has a rapid course with losses as high as 30-50% occurring in 2-4 days. Death is due to anoxia.

DIAGNOSIS:

Microscopic examination will reveal the branched and coenocytic mycelia of the pathogen within the affected gill tissues.

PREVENTION AND CONTROL:

Various chemicals have been used to treat branchiomycosis, which include:

•               malachite green (0.3 mg/L for 24 h)

•               benzalkonium chloride (1-4 ppm active ingredient for 1 h)

•               copper sulfate (100 ppm for 10-30 min)

•               sodium chloride (3-5%)

If an outbreak occurs, feeding of the fish should be stopped and dead fish should be removed from the ponds and buried in a lime pit. To help prevent further outbreaks, the pond should be drained, dried-out and disinfected with quicklime.