Mycoses: Molds and
Fungi
Introductory Comments
 Fungi are members of the Kingdom
Thallophyta
 main characteristic: no chlorophyll
 responsible for a range of serious and
economically important diseases in teleosts
 no photosynthesis = no energy pathways =
parasitic existence
 famous members: icthyoparasites
Fungi Regularly Parasitic in Fish
PHYLUM EUMYCOTA
SP. MASTIGOMYCOTINA
C. Oomycetes
O. Saprolegniales
C. Chytridiomycetes
SP. ZYGOMYCOTINA
O. Chytridiales
O. Entomopthorales
FUNGI IMPERFECTI
C. Hyphomycetes
O. Moniliales
C. Coelomycetes
O. Sphaeropsidales
Saprolegnia
Achyla
Branchiomyces
Dermocystidium
Ichtyophonus
Basidiobolus
Exophiala
Aspergillus
Phoma
Subphylum Eumycota
 The Eumycota are true fungi, having several
subdivisions
 most pathogens are found in the
Mastigomycotina (a subdivision of the
Eumycota)
 they have either a motile sexual stages (e.g.,
Saprolegnia) or non-motile asexual stage
(Achlya)
 the Zygomycotina, another group of true fungi,
have no motile phases, but are still significantly
pathogenic
 of the Mastigomycotina, the most important
pathogens are the Oomycetes
Class Oomycetes
 First fish fungal infection 1748 (Arydon)
 They produce a motile biflagellate spore
(easy dispersal)
 Also produce a thick-walled zoospore by
the fusion of two gametes; thus, oospore
and their name
 usually manifested as hyphae
(1) Saprolegniasis
 Four Orders, but most significant fish pathogens
are within Family Saprolegniaceae
 Saprolegniasis is the term used to describe
infection with Saprolegnia parasitica-declina
complex
 It is typically external, affecting skin and gills,
sometimes eggs
Saprolegniasis
 As mentioned, the adult form is a mass of
filaments known as hyphae
 the mass is called a mycelium (looks like a
wad of cotton in the water)
 hyphae are unique in that they are nonseptate (no divisions)
 the asexual biflagellated zoospores are
thought to initiate most infections
Saprolegniasis: life cycle
Saprolegniasis

Ecology: ubiquitous, most surface fresh waters, limited
to no greater than 2.8 ppt salinity. (Treatment options?)

Can live on dead or live matter, affect only fish which
have been compromised in some way:
1. suppression of immune system (unfavorable temps)
2. injury to skin (trauma)
3. spawning or precocious sexual maturity (thickened
epithelium = more mucus)
4. no seasonal (temperature) restrictions to infections
with eggs
Saprolegniasis
 Clinical signs: gray-white lesions on skin
 lesions start small and circular: spread
 can damage internal organs
 ALL fish susceptible!!
 Unfertilized eggs can be attacked by
hyphae (water hardening)
Saprolegniasis
 Control: good management techniques
 Treatment:
 Malachite green-topical (not approved)
 Bath: 1-2 mg malachite/litre (30 - 60 min.)
 Formalin: Bath: 0.15 to 0.25 mls/litre (60
min.) approved, not as effective…why not
just try salt!!
Saprolegniasis
 More treatments…
 Potassium Permanganate
 Chloramine T
 Methylene blue
 Acetic acid (as a dip @ 5% up to 1 minute)
Saprolegniasis: hyphae
Saprolegniasis
Saprolegniasis
Saprolegniasis
mycelium
Saprolegniasis
Saprolegniasis
Fish eggs with Saprolegniasis
(2) Branchiomycosis
 This disease is commonly referred to as
“gill rot”
 due to massive necrosis of gills
 Branchiomycosis sp. fungus invades gill
blood vessels
 either B. sanguinis (only in gill blood
vessels); carp, goldfish
 or B. demigrans (grows from blood vessels
to tissue); bass, pike, striped bass
Branchiomycosis
 Epizootiology: sudden on-set, rapid
course, high mortality (within two days
sometimes), overall mort’s = 30-50%
 usually when temps above 20oC
 Why? High organic loads, algae, high
temps, high density
 transmission: probably horizontal from
other necrotic gills (spores)
Branchiomycosis
 Clinical features: disease course so fast that
fish are dead before any signs; fish go off
feed, school at surface, become sluggish
 later: necrotic patches on gills (much
clubbing, fusion of lamellae)
 Histopath: hyperplasia of gill epithelium,
fusion of lamellae, massive necrosis
 Control: treatment ineffective due to rapid
on-set; strict hygiene, remove dead fish, don’t
overfeed, fertilize, crowd
Branchiomycosis
Fungal Disease (3):
Ichthyophoniasis (Zygomycotina)
 Originally found by Bruno Hofer in trout in
1893, called disease “the staggers”
 caused by Ichthyophonus hoferi
 thick, fungus-like resting spores
 found in most cold water marine fish populations
 disease transmitted orally
 it is an obligate fish pathogen: life history varies
from host to host
Ichythophoniasis
 Life cycle complicated: produces large number of
endospores and resting spores in most internal organs
 Clinical Features: hyphae are not visible externally,
can affect up to 70% of population if fungus is in
epizootic years
 Histopathology: gray-white lesions of organ, organ
atrophy
 Control: disease transmitted orally
 Don’t feed infected fish to fish (some people feed raw
marine fish offal to hatchery fish)
Ichythophoniasis
Ichythophoniasis
Ichthyophoniasis (I. hoferi)
Fungal Disease (4):
Aspergillomycosis
 Members of the Fungi Imperfecti
 “Fungi imperfecti” = no sexual stage
 Associated with genus, Aspergillus
 Ubiquitous; involved in decay
 Byproducts of degradation of feeds =
aflatoxicosis
Aspergillomycosis
 Recently discovered in farmed fish
(1983), common in Tilapia
 Pathology: abdominal distension,
darkening of color, lethargy; ascites
 Look for hyphae in liver, spleen,
kidney, intestine, swim bladder
 Epizootiology: mortalities of at
least 20% of stock
Shrimp Mycosis: Lagenidium
 This disease largely caused by Lagenidium
callinectes or Sirolpidium sp.
 Two fungal agents can cause rapid mortality
of entire tank
 fungi have similar life cycles, producing
hyphae which spread throughout the body
 major signs: dead or moribund larvae show
obvious hyphae, death in 3-5 days if
untreated
Larval Mycosis:
Lagenidium
 Epizootiology: unknown, possibly
from broodstock, previously infected
batches of larvae, contaminated source
water; spread by motile zoospores
 Diagnosis: simple hyphal structures
on infected animals
 Control: Treflan @ 10 to 100 ppb;
Treflan unstable in water, must be
“dripped” in or re-applied every 5-8
hrs; disinfection of tank and apparati
Lagenidium callinectes
Shrimp Mycosis: Fusarium sp.
 Fungi affecting adults (fungi imperfecti)
 Causes “fusariosis”
 Largely associated with broodstock,
particularly of Farfantepenaeus japonicus
and Litopenaeus stylirostris
 L. vannamei appears fairly resistant
Fusarium sp.
 Fusariosis is a problem when…
 shrimp are typically older
 cuticle wounded
 improper sanitation
 Major Signs: melanized (splotches)
 often found on tips of appendages
Fusarium sp.
 Mortality rates of infected shrimp vary due to
complex relationship between host, fungus and
secondary bacterial infection
 stress + infection = mortality (esp. shipping)
 Transmission: Fusarium is naturally-occurring
fungus of decaying organic matter, produces
non-motile infective spores (macroconidia)
 infection is passive through wound, hyphae
penetrate underlying tissues
Fusarium sp.
 Diagnosis: presence of lesions in
broodstock or adults, demonstration of
hyphae
 Control Strategies: no practical
treatment, prevention a matter of proper
husbandry, sanitation, adequate facilities
 Avoid rough handling
 Remove infected broodstock, adults
Fusarium sp.