Saprolegnia spp

From Fish
Saprolegnia spp infecting a fish

Saprolegnia is often used as a collective name for a fungal infection of fish caused by several genera (such as Saprolegnia, Achyla, Aphanomyces and Dictyuchus) predominantly of the order Saprolegniales (family Saprolegniaceae)[1][2]. Lesions may have mixed infections. While characteristics of the sporangium formation and zoospore release are important for determination of saprolegnian genera, details of the reproductive organs, the oogonia and the antheridia are important criteria for specific differentiation. Mycelia recovered from fish contain, however, only asexual reproductive organs (oval elongated sporangia which contain biflagellated zoopores).

Saprolegniaceae may be cultured on any nutritive agar medium plate with the addition of antibiotics (such as Sabouraud's agar). A specific methodology for isolation of Saprolegnia has been devised by Willoughby & Pickering[3]. All these cultures yield only asexual generations. Sexual generations may be obtained only through specialised culture methods[4].

The genus Saprolegnia has oblong sporangia and is also recognised by its branched, non-septate multinucleated mycelium. The released zoospores typically swim away. In the genus Achyla the spores encyst at the mouth of the sporangium where they form a hollow ball. Encystment at the mouth of the sporangium also occurs in Aphanomyces.

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. 159 pp.
  2. Chien, Chiu-Yuan, 1981. Fungal diseases of fresh water fish in Taiwan. Nation. Sci. Counc. (Republic of China) Symp., Ser. 3: 33–45
  3. Willoughby, L.G. & Pickering, A.D., (1977) Viable Saprolegniaceae spores on the epidermis of the salmonid fish Salmo trutta and Salvelinus alpinus. Trans Br Mycol Soc 68:91–95
  4. 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. 159 pp