Infectious diseases of fishes in the MDB, including...
Transcript of Infectious diseases of fishes in the MDB, including...
Outline of talk
• Introduction • Disease research • Common/important diseases • Fungal diseases • EUS
– the disease – Australia, MDB – June 2010 – conclusions and recommendations
• Observation and collections in the field • Zoonoses
Diseases do cause mortalities of native fish !!
Dead silver perch on a farm - winter sap
Dead Murray cod in Lake Mulwala September 1980 – chilodonellosis
Broad categories of diseases
• Infectious diseases – infectious agents or pathogens – protozoans – fungi – bacteria – viruses – worms
• Non-infectious diseases – environmental factors – low DO – high and low pH – high ammonia, hydrogen sulphide
Diseases in the MDB
• Few reports in native fish in the wild • EHN and GUD in exotic species
– Richard Whittington – GUD in SP
• Well know in aquaculture
– SP – MC – Rowland, Callinan and Ingram
Disease research – aquaculture • Inland Fisheries Research Station/Narrandera Fisheries
Centre – research into hatchery production; since 1978 – MC, TC, GP, SP – hatchery industry (1982/83)
• Grafton Aquaculture Centre – SP – 1990 - 2010
• Snobs Creek – MC, TC, MP – 1980 – 2010
• Native fish aquaculture industry – inland species (SP, MC, GP) – 500 tonnes annually – > 3 million fingerlings – $6.5 million
Type of organism Pathogen Disease Comment
Protozoan Ichthyophthirius multifiliis
Chilodonella hexasticha
Trichodina sp.
Ichthyobodo necator
Tetrahymena sp.
Coccidia sp.
Ichthyophthiriosis (white
spot, ich)
Chilodonellosis
Trichodinosis
Ichthyobodosis
Tetrahymenosis
Coccidiosis
Common; acute
Common; acute
Common; chronic
Not common; potentially acute
Rare
Rare
Myxosporidian Henneguya sp. Uncommon
Ecto-commensal
ciliate Ambiphyra sp. Rare
Monogenean Lepidotrema bidyana
Gyrodactylus sp. Gill flukes
Gill flukes Common; chronic
Rare
Copepod Ergasilus sp.
Lernaea sp. Ergasilus
Anchor worm Rare
Uncommon eastern drainage; may be
common in parts of western drainage
where carp in water supply
Fungus (mold) Saprolegnia parasitica
Aphanomyces invadans
Fungus
Winter saprolegniosis
Epizootic ulcerative
syndrome
Ubiquitous pathogen
Acute on some farms
Eastern drainage only; not common;
notifiable disease
Bacteria Flexibacter columnaris
Flexibacter, Aeromonas, Pseudomonas
Aeromonas salmonicida nova
Streptococcis iniae
Mycobacterium spp.
Aeromonas hydrophila and other spp.
Chlamydia-like bacteria
Columnaris
Tail rot, fin rot
Goldfish ulcer disease
Streptococcosis
Mycobacteriosis
Aeromonad dermatitis
Epitheliocystis
Bacterial diseases are uncommon in
silver perch culture
Virus Epizootic Haematopoietic Necrosis
Virus (EHNV)
Epizootic haematopoietic
necrosis (EHN) Not recorded naturally in silver
perch
Infectious diseases and pathogens of silver perch
Common diseases and pathogens
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Type of pathogen
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Acute diseases – ich and chilodonellosis (GAC – 20 years)
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Common/important diseases Protozoan diseases
• Ichthyophthiriosis – Ich, white spot
• Freshwater fish world-wide
– MC, SP
• Ichthyophthirius multifiliis
– ciliate protozoan
• Acute disease – can cause 100% mortality within days
• Some natural immunity
Life cycle of Ichthyophthirius multifiliis
Temperature dependent: 10°C 20 days 12° - 15°C 13 – 14 days 20° - 25°C 3 – 7 days
Chilodonellosis
• Chilodonella hexasticha – ciliate protozoan – oval shape – 50 – 70 µm – cyst stage
• Common • Acute
– rapid, high mortality – SP, MC, herring
Anchor worm – Lernaea sp.
• Copepod – life cycle – temperature-dependent
• Female infestive – modified head – under skin
• Effects – lesions – infections – reduced growth – loss of condition – inhibits reproduction – morbidity – mortality
Other pathogens tapeworm round worm Ergasilus (copepod)
Henneguya (myxosporidian) Gill fluke (monogenean trematode)
Bacterial and viral diseases
• No viral diseases recorded – wild or fish farms – SP 100% mort EHN in lab
• Bacterial diseases (< 3%) – columnaris – fin rot (tail rot) – streptococcosis – mycobacteriosis – Aeromonad dermatitis – goldfish ulcer disease – epitheliocystis
columnaris
tail rot
GUD
Bacterial diseases
• External lesions – red spots; ulcers
• Internal lesions – in organs
• Exophthalmia – pop-eye
• Fluid in body cavity • Pathology and bacteriology
Aquatic fungi
• Molds – saprophytic – feed on dead matter
• Ubiquitous • Reproduction
– complex, variable – spores
Fungal hyphae and spores
Fungus on Murray cod eggs
Fungus on tail
Fungal diseases • Ubiquitous • All/most species freshwater fish
– warmwater and coldwater
• Saprolegnia parasitica
• Primary and secondary pathogens
– invade and damage skin
• Causative factors
– physical damage – parasites – stress – crowding – immune suppression
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Morts
Rapid drop in temp in winter: 6ºC in 10 days (day 1 – 21st May)
Total mortality silver perch
Winter saprolegniosis
Winter sap – predisposing factors
• Low water temperatures (< 15ºC) • Rapid decline (4º - 6ºC in 5 – 10 days) • Suppression of immune system • Ecto-parasites • Handling damage and stress
– partial harvests
• Poor water quality – high organic load – high ammonia – low DO – poor circulation in ponds
Epizootic ulcerative syndrome (EUS)
• Ulcerative disease – freshwater and estuarine fish
• Fungus – Aphanomyces invadans
• Invasive, rapidly spreading • Spores
– infect, germinate – grow in muscle - outwards – dermal lesions and ulcers
• Reportable disease • Australia, Asia, Africa, USA • Over 100 species
– high mortalities – varying susceptibility – carp and tilapia resistant
EUS - Australia
• First reported 1972 – Bundaberg disease – sea mullet
• Spread south 1980s – Clarence and Richmond systems – regular outbreaks – mullet, bream, whiting, flathead
• Eastern, coastal drainages – Bundaberg to Hawkesbury – Northern Territory, Western Australia
• Not MDB – prior to 2008
• Silver perch – farms in eastern drainage – severe in fingerlings
Outbreak of ulcerative disease – June 2010 • Barwon-Darling • 200 km • 30 locations • 5 species (14) • Prevalence
– 10%
a) b)
c) d)
e) f)
a) b)
c) d)
e) f)
bony herring (16%)
golden perch (8%)
Murray cod (5%)
spangled perch (21%)
common carp (1%)
EUS diagnosed
• Gross appearance of lesions and ulcers – EUS-distinctive – characteristic stages of progression
• Histopathology – penetrating fungal hyphae – thick-walled, non-septate – granulomas (healing, repair)
• Polymerase chain reaction (PCR) – DNA; species-specific for Aphanomyces invadans
EUS – a new disease in MDB??
• No clinical evidence – prior to 2008
• Large number of hosts – herring, GP, MC, spangled perch, carp
• Large area (200 km) • Severe ulceration in each species • Individual fish with numerous and large lesions
and ulcers
Environmental factors – flow and temp
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Environmental factors
• 2010 outbreak – followed high flows – low temps (< 15°C) – pH (7.3 – 8.7) – DO (4.2 – 10.6)
• Other EUS outbreaks linked to: – heavy rainfall, high flows – low pH (< 6), high pH (> 9) – low DO – declining alkalinity, conductivity
• Presence of the pathogen A. invadans
Low temperatures (< 16°C) in warmwater fishes
• Immune suppression • Reduced mucus production • Enable fungi to act as primary pathogen • Winter saprolegniosis
– SP – herring – eel-tail catfish – channel catfish (USA)
Introduction of pathogens
• Spread of diseases a world-wide problem • GUD
– 1974 Japan to Australia – goldfish farms to wild
• Anchor worm (Lernaea sp.) – carp to native fish – throughout MDB
• SP, MC, GP – cultured in eastern drainage – translocation to MDB?
Conclusions and recommendations
• EUS in the MDB – an invasive disease that will spread
• Surveillance, reporting and diagnosis – determine distribution, identify hosts, susceptibility
• No translocation of fish from eastern drainages – ceased in NSW
• Restrict movement of fish – out of Barwon-Darling – aquaculture broodfish, research
• Disinfect equipment used in B-D • Implement NSW HQAP
Observations in the field moribund fish
abnormal behaviour, e.g. flashing
dead fish
lesions and ulcers
Collection of samples in the field
• Microscopic examination • Collection for histopathology, bacteriology • Moribund fish
– best for disease diagnosis – some parasites leave dead fish – contamination by bacteria
• Live/moribund – plastic bags (heavy duty) or bins – oxygen and water; sealed – keep live – chilled on ice in esky – cut out gills and/or section of skin/muscle
• Formalin (10% buffered) – excised tissues or whole fish – plastic containers – label and data
Zoonoses
• Diseases transmitted to humans – immunosuppressed, elderly, children
• Spine punctures; open wounds; ingestion • Bacterial pathogens most common
– Mycobacterium, Aeromonas, Streptococcus, Vibrio
• Symptoms – skin inflammation, infection, swelling, stiffness, necrosis,
septicaemia, arthritis
• Precautions and actions – wear gloves – take care handling diseased fish – seek medical attention