Fungal Diseases on Fishes

FUNGAL DISEASES
Reported by:
JULY B. ARIÑEZ

Fungi
• Heterotrophic straminipilous organisms
• Eukaryotic
• Can be unicellular or multicellular
• Cell walls made of chitin
• Contain no chlorophyll
• Filamentous
• Either be saprobes or parasites

Structure and Reproduction
• Have filaments called hyphae that can either be septate or
non-septate
• Networks of hyphae are called mycelium
• Body – soma or thallus (capable of growth)
* Zoosporic fungi or straminipilous fungi cause most fungal disease
of aquatic animals.

CONTRIBUTING FACTORS
Stress factors such as:
•Mechanical injury after handling
•Exposure to extreme pH levels
•Prolonged exposure to low water temperatures
•Lack of food
•Excessive use of chemotherapeutants
•Presence of other microbial infections (e.g.
bacterial, viral) increase

Saprolegniosis (Saprolegniasis)
a.) Causative Agents:
Saprolegnia spp., Achlya spp., and Aphanomyces spp.
b.) Species affected: Freshwater fish (carps and goldfish)
c.) Signs:
1. Formations of white cottony growth on fish eggs or
tissues.
2. Fish becomes lethargic, tires easily and respond
slowly to stimuli
3. Histopathologically, rapid destruction of epidermis
with slight inflammation are observed.
Figure 1. Mycelial filaments of
Saprolegnia sp. on the gills of red
drum with saprolegniasis (fresh
mount, 100x)

d.) Diagnosis:
Microscopic examination reveals the characteristic hyaline and coenocytic mycelia
Numerous sporangia – tentative generic identification.
e.) Prevention and Control:
Bath treatments of chemotherapeutants such as:
• Zinc-free malachite green (67 mg/L for 1 min; 0.2 mg/L for 1 h)
• Sodium chloride (22 g/L for 30 min; 30 g/L for 10 min)
• Formalin (0.4-0.5 ml/L 30% formaldehyde for 1 h)
• Hydrogen peroxide and increasing the salinity

Fig. 1. (A) African cichlid with Saprolegniasis. Note dark areas (hemorrhages/ulcers)
at edges of fungal growth. (B) Life cycle of water molds (From Noga EJ. Fungal and
algal diseases of temperate freshwater and estuarine fishes. In: Stoskopf M

Ulcerative Epizootic Syndrome (UES)
a.) Causative agent:
• Aphanomyces invadans, rhabdovirus and
Aeromonas hydrophila
• Straminipilous organisms such as
Aphanomyces strains, Saprolegnia spp., and
Pythium spp.
b.) Species affected: <30 freshwater fish
species (snakeheads, catfish, gourami, goby
and etc.)
Figure 2. Fungal hyphae (black stain) in
the connective tissue of the ovary of EUS-
infected snakehead, Ophicephalus striatus.
(Gomori methenamine silver stain, 100x)

Ulcerative Epizootic Syndrome (EUS)
c.) Signs:
1. Darker discoloration and loss of appetite
2. Fish may be hyperactive with very jerky movements
3. Ulcerative lesions throughout the fish’s body
4. Fish becomes lethargic in later stages with exposed
head, bone tissues, visceral organs or vertebral
column, tail erosion
5. Histopathologically, massive infiltration of the tissues,
severe necrosis and minimal inflammation can be
observed.

d.) Diagnosis
Isolation of A. invadans from internal tissues.
- common among wild fish stocks, prevent the entry of any infected fish in
the area
a.) Eradication of the causative agent (e.g. fungi)
b.) Proper management by reducing stocking densities during
prevalence of EUS
c.) Farming of EUS-resistant fish species (e.g. tilapia)
d.) Application of treatments like: 5 ppm Coptrol (a chelated copper
compound or 0.1 mg/L malachite green.

Fig. 3 Atlantic menhaden (Brevoortia tyrannus) with deep ulceration caused
by Aphanyomyces invadans. (Courtesy of Christine Densmore, National Fish
Health Research Laboratory, US Geological Survey, Kearneysville, WV.)

Branchiomycosis (Gill rot)
a.) Causative agents: Branchiomyces spp.
b.) Species affected: Carps, goldfish, eels
c.) Signs:
1. Gills become pale with brownish areas
2. Necrotic areas susceptible for saprolegnian infections.
3. Gill fungal hyphae obstruct blood circulation
4. Necrosis, lamellar epithelial cells and lamellar fusion proliferate
d.) Diagnosis:
Microscopic examination (branched and coenocytic mycelia of pathogen

Treatments with the use of chemicals:
• 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%)
Outbreaks = feeding of the fish should be stopped
dead fish should be removed from the ponds and buried in a lime pit.
Prevent outbreaks = pond should be drained, dried-out and disinfected with
quicklime.

Figure 5. Carp with branchiomycosis (gill mycosis):
Photo Bayerische Biologische Versuchsanstalt (Adopted
from Fish pathology by Reichenbach-Klinke's)
Fig. 6. Branchiomyces species, intravascular, located at the base of
the gill arch. GA, base of gill arch. (B) Branchiomyces species; GC,
gill cartilage, support structure of primary lamellae. (Courtesy of
Lester Khoo, University of Pennsylvania, Philadelphia.)

Ichthyophoniasis (Ichthyosporidiosis)
a.) Causative agent: Ichthyophonus sp. (Ichthyosporidium sp.)
b.) Species affected: Groupers, trouts, flounders, herrings and cods
c.) Signs:
1. Erratic swimming behavior and swelling of the abdomen.
2. Spleen, liver and kidney become swollen with numerous
whitish nodules (2mm in diameter)
3. fish lose their appetite and become lean and anemic.
4. loss of apetite, emaciation, lethargy and color changes
5. Rough skin “sandpaper effect”
d.) Diagnosis:
Microscope examination: nodule (early cysts, develop cysts and fungal hyphae

Ichthyophoniasis (Ichthyosporidiosis)
no known treatment
occur when fed with raw trash fish (pathogen)
carefully avoided to avoid trash fish

Figure 7. Juvenile Pacific herring demonstrating external
signs of ichthyophoniasis including pigmented skin ulcers
and general emaciation. Photo: P. Hershberger, U.S.
Geological Survey.
Figure 8. Rainbow trout with ichthyophoniasis demonstrating
petechial hemorrhages on the skin surface. Photo: Dr. Scott
LaPatra, Clear Springs Foods, Inc.

Figure 8. Ichthyophonus sp. in Dicentrarchus labrax.
Scale bars = 20 µm (Bobadilla and Pellitero, 1990)
Figure 9. Characteristic macroscopic hepatic lesions of
Ichthyophonus of a heavily infected yellowtail flounder. The liver is
covered with small firm white, clear or yellowish nodules (I). Also
note the severe epicarditis and pericarditis of the heart (II).

Major Fungal Disease of Crustaceans

Larval Mycosis
a.) Causative Agents: Lagenidium spp.,
Sirolpidium spp., Haliphthoros spp.
b.) Species affected: All Penaeus species, crabs
(e.g. Scylla serrata)
c.) Signs:
1. Onset of Larval mortalities in shrimps
(mortality of 20-100% within 48-72 h after
onset of infection)
2. Progressive systemic mycosis
accompanied by little or no host inflammatory
response.
Figure 3. Lagenidium infection in crustacean
larvae. A – Larva of Penaeus monodon heavily
infested with the fungus. B – Infected Scylla
serrata larva in brain-heart-infusion (BHI) broth
after 2 days (fresh mount, 40x)

Larval Mycosis
d.) Diagnosis:
Microscopic examination (extensive, non-septate, highly branched
fungal mycelia)
Specialized hyphae or discharge tubes (identification of causative
agent)
• Classification of the causative organism is dependent upon the microscopic
examination of sporogenesis as follows:
1. Lagenidium – zoospores are released from terminal vesicle
2. Sirolpidium and Haliphthoros – absence of terminal vesicles;
zoospores are released through discharge tubes formed by the zoosporangia.

Larval Mycosis
Figure 4. Filaments of Lagenidium in the tail of Penaeus
monodon larva (arrows). Zoospores in a vesicle (arrowhead)
are about to be released by the fungus (fresh mount, 40x)
Figure 5. Zoosporangial development of
Haliphthoros sp. by hyphal fragmentation
(arrowheads=discharge tubes) (fresh mount, 200x)

Larval Mycosis
Disinfection of contaminated larval rearing tanks
Chlorination and/or filtration of the incoming water
Recommended chemicals for therapeutic and prophylactic treatments:
• 0.2 ppm Treflan
• 1-10 ppm formalin
• egg disinfection with 20 ppm detergent followed by
thorough rinsing before hatching
• Salinities 7-15 ppt – control motile zoospores

Black Gill Disease (Fusarium Disease)
a.) Causative agent: Fusarium solani
b.) Species affected: All Penaeus species
c.) Signs:
1. Appearance of black spots
2. Infection usually starts on damaged
tissues such as wounds, gills damaged from
chemical treatments or pollutants, and
lesions.
3.Lesions may also serve as a route of
entry for other opportunistic pathogens.
Figure 6. Canoe-shaped macroconidia
of Fusarium sp. (fresh mount, 400x)

d.) Diagnosis:
Microscopic examination of infected tissues (canoe-shaped
macroconidia)
Fusarium spp. are soil fungi.
Fusarium solani - opportunistic pathogen of penaeids (stresses or
overcrowding.
Elimination of sources of Fusarium conidiophores and destruction
of infected individuals. Several fungicides show promise in vitro but none
proved to be effective in actual field trials.

Fig. 10. Parrotfish with Fusarium infection. Note ulcer on
ventrolateral aspect extending into deep musculature. (Courtesy of
Scott Terrell, University of Florida, Gainesville, FL.)
Fig. 11. Closer view of deep ulcer in parrotfish.
(Courtesy of Scott Terrell, University of Florida,
Gainesville, FL.)

Aflatoxicosis (Red Disease)
a.) Causative agent:
Aflatoxin produced by Aspergillus flavus and other Aspergillus spp.
(contaminants of not-properly stored or expired feeds)
b.) Species affected: Penaeus monodon or other Penaeus spp.
c.) Signs:
1. Yellowish or reddish discoloration of the shrimp body and appendages.
2. Lethargic with weak swimming activity near pond dikes.
3. Soft shelling
4. Retarded growth
5. Histopathologically, necrosis in the tubule epithelium can be observed.

Aflatoxicosis (Red Disease)
d.) Diagnosis:
• Confirmation is through bychemical
analysis for the presence of aflatoxin in
the suspected feed/ingredient.
• Do not use moldy feeds.
• Feeds should be properly stored (for not
more than 6 months) in dry and well-
ventilated areas to prevent Figure 7. Mass of sporangia of Aspergillus
sp. on contaminated feed particles (fresh
mount, 200x)

References:
• Lavilla-Pitogo CR, de la Peña LD. 2004. Diseases in farmed mud crab Scylla
spp.: Diagnosis, Prevention and Control. SEAFDEC Aquaculture
Department, Iloilo, Philippines, 89 p.
• Nagasawa, K. and E.R. Cruz-Lacierda (eds.) 2004. Diseases of cultured
groupers. Southeast Asian Fisheries Development Center, Aquaculture
Department, Iloilo, Philippines, 81 p.
• Leaño, E. M. (2001). Fungal diseases. In G. D. Lio-Po, C. R. Lavilla, & E. R.
Cruz-Lacierda (Eds.), Health management in aquaculture (pp. 43-53).
Tigbauan, Iloilo, Philippines: SEAFDEC Aquaculture Department.
• Roy P.E. Yanong, VMD. (2003). Fungal diseases in of fish. Vet Clin Exot Anim
6, pp. 377–400.
• Sitja-Bobadilla, A. and Alvarez-Pellitero, P. 1990. First report of
Ichthyophonus disease in wild and cultured sea bass Dicentrarchus labrax
from the Spanish Mediterranean area. Dis. aquat. Org., Vol. 8. pp. 145-150.

Fungal Diseases on Fishes

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