Mycoses: Molds and Fungi Introductory Comments Fungi are members of the Kingdom Thallophyta main characteristic: no chlorophyll responsible for a range of.
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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.