Transcript Document 7362695

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 example of a fungal infection noted in
fish was illustrated by Arderon in 1748
 as mentioned, 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
 Although there are four Orders within the Class
Oomycetes, almost all of the 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

Ecology: ubiquitous, most surface fresh waters,
limited to no greater than 2.8 ppt
 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 (temp) restrictions to infections with
eggs
Saprolegniasis
 Clinical features: seen as gray-white
lesions (patches) on skin, could be colored
due to what’s in culture water
 lesions start small and circular, but spread
 can sometimes damage internal organs
 all fish are susceptible
 only unfertilized eggs can be penetrated by
hyphae
Saprolegniasis
 Control: for the fish, use good
management techniques, avoid
predisposing factors (feed, injury, water
quality esp. temp)
 Treatment: malachite green as topical
disinfectant (not approved), formalin is
approved but not as effective
Saprolegniasis: life cycle
Saprolegniasis: hyphae
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 also classified as
Ichthyosporidium hoferi
 usually seen as thick, fungus-like resting spores
 endemic in most feral 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
 usually comes from other fish in population
 Clinical Features: hyphae are not visible externally,
can affect up to 70% of population is fungus is in
epizootic years
 Histopathology: signs depend on host, organs
involved; generally, as gray-white lesions of organ,
organ atrophy
 Control: disease transmitted orally; obviously, 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
 These agents are members of the Fungi
Imperfecti
 “Fungi imperfecti” simply means you can’t
find sexual stages in the life cycle of the
fungus
 associated with genus, Aspergillus (those of
you who have had Aquatic Nutrition
remember this guy, right?!)
 the Aspergilli are ubiquitous and typically
involved in decay processes
 byproducts of degradation of feeds =
aflatoxicosis
Aspergillomycosis
 Only recently discovered as a pathogen of
farmed fish (1983)
 largely described for cultured Tilapia
 usually seen after any stress in terms of
management of fish in ponds (partial harvest,
weighing, etc.)
 Pathology: abdominal distension, darkening of
color, lethargy; incision of body cavity =
copious amounts of fluid
 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 due to obvious
hyphal structures in 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.
 We have already mentioned Lagenidium
callinectes and Sirolpidium sp.
 These were agents of larval mycosis
 One common fungi affecting adults is Fusarium
sp., member of fungi imperfecti
 Causes disease known as fusariosis
 largely associated with broodstock, particularly
of Farfantepenaeus japonicus and Litopenaeus
stylirostris
 L. vannamei appears fairly resistant
Fusarium sp.
 Fusariosis is a problem when several
contributing factors are present:
 age: shrimp are typically older (adult,
broodstock)
 cuticle wounding: due to rough handling,
crowding, rough container surfaces
 improper sanitation
 Major Signs: melanized, raised or nodular
lesions on cuticle, appendages, gills (fungus
cannot penetrate intact cuticle)
 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 in combination with infection can cause
increased handling mortality (esp. shipping)
 Transmission: Fusarium is naturally-occurring
fungus of decaying organic matter, produces
non-motile infective spores (macroconidia)
 infection is passive through wound, conidia
germinate and produce hyphae which penetrate
underlying tissues
Fusarium sp.
 Diagnosis: presence of lesions in broodstock or
adults, demonstration of hyphae, canoe-shaped
macroconidia, culture on std mycological media
 Control Strategies: no practical treatment,
prevention a matter of proper husbandry,
sanitation, adequate facilities
 avoid procedures/conditions leading to cuticle
damage
 cull out infected broodstock, adults
Fusarium sp.