|
B. Destructive Fungal Parasites 4. Fungal Diseases of Fish, Shellfish and Amphibians
|
|
|
4. Fungal Diseases of Fish and Shellfish Many species of fungi cause diseases in a variety of aquatic animals. Saprolegniasis is an external infection of fish caused by the water mold Saprolegnia diclina, but species of a number of other genera of water molds have also been implicated. These are common as fuzzy white lesions on scale fish in warmer waters (Fig. 14-30), and skin lesion in winter kill in catfish (Fig. 14-31).
Fig. 14-30. A small minnow with a severe infection of Saprolegnia. (Provided by Ruth Francis-Floyd).
Fig. 14-31. Skin lesions and winter kill of catfish are also caused by species of Saprolegnia. (Provided by Andy Goodman). On the Atlantic salmon, however, the lesions may become more than 5 cm across. A fungal disease in the gills, referred to as gill rot (Fig. 14-32), is also caused by Saprolegnia, and by a number of species of Branchiomyces.
Fig. 14-32. Gill rot in catfish caused by a species of Saprolegnia. (Provided by Andy Goodman). It has been reported on 29 species of fish (Chacko, 1991. Handb. Appl. Mycol. 2: 735-755). Over the years a number of conidial fungi have been isolated from lesions on fish, as for example, species of Penicillium and Cladosporium (Fig. 14-33) infecting the swim bladder of red snapper.
Fig. 14-33. A dissected red snapper showing the swim bladder (arrow) infected with both Penicillium and Cladosporium. (Provided by Robin Overstreet).
|
Infection of eggs and larvae of the blue
crab is caused by another water mold, Lagenidium
callinectes. As high as 95% infection has been found in populations
of crabs off the North Carolina coast. Larvae become sluggish and cannot
swim and many times eggs will not hatch. Crayfish
are also parasitized by various water molds, but predominantly species
of Saprolegnia and Aphanomyces.
A crawfish plague caused by A.
astaci decimated the industry in eastern Russia. The fungus
primarily targets the connective tissues of the crawfish. Fortunately,
North American crawfish appear resistant to this fungus. Lobsters
become infected with species of Lagenidium
and Halipthoros, resulting in
the larvae becoming white and death occurring within 24-48 hours. A
large number of water molds, such as Sirolpidium (Fig. 14-33a) are known to infect shrimp,
but Lagenidium callinectes has
been studied most extensively. While infections are largely on the
larval stages, the fungus can also infect abdominal muscles. The water
mold Sirolpidium zoophthorum
has been shown to destroy whole populations of clams
and oysters (Sindermann, 1977. Crustacean diseases. Elsevier Sci.
Pub. N.Y.).
Fig. 14-33a. A larval shrimp showing hyphae of Sirolpidium inside abdominal appendages. (Provided by Robin Overstreet). Although poorly studied, amphibians and reptiles are not immune from fungal attack. In certain habitats, frogs have been found infested with a species of Achlya (Fig. 14-33b), and here in Florida herpetologists have found numerous infections of pigmy rattlesnake caused by Sporothrix schenckii (Fig. 14-33c).
Fig. 14-33b. A frog with a heavy growth of a species of Achlya. (Provided by Mel Fuller)
Fig. 14-33c. Head of a pygmy rattlesnake with necrotic lesions are caused by Sporothrix schenckii. (Provided by Joe Cheatwood) |
