Brachiomycosis

From Fish
Brachiomycosis on the gills of a fish
Carp gills affected by brachiomycosis

Branchiomycosis is a fungal disease of gill tissue characterized by respiratory distress and gill necrosis.

The causative agents are Branchiomyces sanguinis and B demigrans, which are opportunistic pathogens found in decaying organic materials in the aquatic environment. Branchiomycosis typically occurs in warm ponds (water temperature >20°C) with high organic loads. It seems endemic in eastern Europe, where it is an important problem in food fish industries; it is also occasionally reported in the USA.

Clinical signs

Affected fish show signs typical of hypoxia. Gross examination of gills reveals necrotic, mottled, and pale tissue.

Diagnosis

A presumptive diagnosis can be made by observation of characteristic aseptate, branched hyphae in gill lamellae.

Branchiomyces in carp gills is usually localised in the blood vessels, the efferent branchial vessels and the capillaries, producing branched coenocytic hyphae capable of producing aplanospores by endogenous cleavage[1]. In eels branchiomycosis hyphae and spores spread to visceral organs[2].

Infection is probably by spores liberated from the necrotic tissue, but the exact route by which fish contract infection is unknown.

Pathology Infection in the blood vessels of the gill causes blockage, haemostasis and thromboses which consequently cause extensive necrosis of the gill filaments. Areas of the gill filaments turn brown, due to haemorrhages and thromboses, and grey as a result of ischemia. The process is fast and is accompanied by proliferation of the gill epithelium with resulting adhesions of the filaments (Richards, 1978; Neish & Hughes, 1980). In eels, lesions containing hyphae and spores occur in the epicardium and the spleen.

Treatment

Branchiomycosis is prevented by avoiding predisposing conditions. Ponds that are at risk should be kept as clean as possible, and stocking rates decreased when water temperatures approach 20°C.

Recommended treatments for infected fish are, application of 0.3 ppm Malachite green per 24h, 1.2 ppm copper sulphate into the pond or as a quick dip (10–30 min.) at 100 ppm, or a dip in 3–5% NaCI. However, the efficacy of such treatments is not well established. As a prophylactic treatment, it has been recommended to treat earth ponds prior to stocking as a measure for water quality, with 150–200 kg ha-1 Calcium oxide (quick lime) or 8 to 12 kg Copper sulphate ha-1 for 0.5 and 1 m deep ponds respectively[3].

References

  1. Neish, G.A. & Hughes, G.C., (1980) Fungal diseases of Fishes. S.F. Snieszko & Axelrod, H.R. (ed.) Diseases of Fishes, Book 6. T.F.H. Publ. Inc. Ltd. pp:159
  2. Chien, Chau-Heng, Miyazaki, T. & Kubota, S.S., (1978) The histopathology of branchyomycosis of eel in Taiwan. JCRR Fish Ser 34:97–98
  3. Sarig, S., (1971) The prevention and treatment of diseases of warmwater fish under subtropical conditions, with special emphasis on intensive fish farming. T.F.H. Publications Inc., Jersey City, N.J. P:127