Gill Health in Finfish Aquaculture
Dr. Hamish Rodger
Gill Health in Finfish Aquaculture
Outline
Gill disease background
Aetiologies of gill disease
Pathologies
Control & treatments
Gill Health in Finfish Aquaculture
Main gill functions
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Gas exchange (O2, CO2)
Acid – base balance
Osmoregulation
Excretion of nitrogenous waste products (mainly NH3)
O2, CO2 sensors (neurons)
© H. Rodger
Gill Health in Finfish Aquaculture
Gill disorders – finfish farms
• UK – amoebic gill disease (AGD), proliferative/hyperplastic gill
disease, algae, jellyfish
• Norway – proliferative gill inflammation (PGI), AGD, pox virus
• Australia & Japan – AGD, plus…
• Chile & USA – AGD, harmful algae, others?
• Canada – harmful algae, Loma sp., PGD-type?
Gill Health in Finfish Aquaculture
Causes of gill disorders
Gill Health in Finfish Aquaculture
Causes of gill disease
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Harmful algal blooms (physical, toxins or deoxygenation)
Harmful zooplankton swarms (nematocysts)
Amoebic gill disease & other parasites
Bacterial gill disease
(Tenacibaculum sp., others)
Viruses
Fungi
Chemical (hydrogen sulphide,
hydrogen peroxide)
Multiple and/or sequential
© H. Rodger
Exposure to pathogens
Primary insult to gills
(phytoplankton,
zooplankton, others)
Change in environmental
conditions
Infestation or infection
Colonisation of gills by
harmful bacteria
Direct pathology &
impact
Infestation by protozoans
(costia, trichodina)
Proliferation of
parasites, other
bacteria
Gill disease (AGD, pox
virus, etc.)
Bacterial gill
disease/epitheliocystis/P
GI or D?
Site A 08GS1 Weekly Mortality Per Pen
30.0
% Weekly Mortality
25.0
C1
C2
20.0
C3
C4
15.0
10.0
5.0
0.0
Hyperplasia, fusion, necrosis & epitheliocystis
Tenacibaculum sp. bacteria
Trichodina, marine costia, amoeba
Gill Health in Finfish Aquaculture
Harmful algae
Gill Health in Finfish Aquaculture
Harmful algae blooms (marine)
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> 200 harmful species
Karenia mikimoti (dinoflagellate)
Noctiluca scintillans (dinoflagellate)
Pseudo-nitzschia sp.
Chaetoceros sp. (diatom)
Gill Health in Finfish Aquaculture
Harmful algae blooms (HAB); clinical signs
Fragile, bleeding gills,
inappetance, behaviour
change, visibility
Photo by A. MacAteer
Gill Health in Finfish Aquaculture
Harmful algae blooms (HAB); gross pathology
© H. Rodger
Diffuse necrosis,
haemorrhages
© H. Rodger
Increased mucus
Gill Health in Finfish Aquaculture
Harmful algae blooms (HAB); histopathology
Diffuse epithelial
apposition,
sloughing &
necrosis (Karenia
mikimotoi)
© H. Rodger
© H. Rodger
Gill Health in Finfish Aquaculture
Harmful jellyfish or zooplankton pathology
Gill Health in Finfish Aquaculture
What are Jellyfish?
jellyfish
Little jellyfish
(Scyphomedusae)
(Hydromedusae)
Siphonophores
Comb jellies
(Siphonophores)
(Ctenophores)
Gill Health in Finfish Aquaculture
Harmful jellyfish or zooplankton
pathology
Stinging cells (nematocysts)
- Mechanical damage
- Toxic Damage
Gill Health in Finfish Aquaculture
Hydroids (Ectopleura larynx) & biofouling organisms
Gill Health in Finfish Aquaculture
Jellyfish pathology
Muggiaea atlantica & Phialella sp.
Aurelia aurita
Gill Health in Finfish Aquaculture
Harmful zooplankton gill histopathology
Focal epithelial necrosis, sloughing and
haemorrhage/thrombosis or haemolysis
(Aurelia aurita)
Concurrent or secondary bacterial
infections
Progression or healing?
© H. Rodger
Finfish
Potential
vectors for
Aquaculture
Phialella
quadrata and Pelagia noctiluca: implicated as vectors of the
pathogens?
bacterial disease Tenacibaculum maritimum
© H. RODGER
Muggiaea atlantica
© H. Rodger
Delannoy et al. 2011
Finfish
Aquaculture
Gill parasites
Finfish
Amoebic gill disease
Aquaculture
Neoparamoeba perurans
© H. Rodger
© H. Rodger
Gills affected with Ichthyobodo sp. & fungi (Saprolegnia sp.)
• Tenacibaculum sp.
Bacteria
• T. maritimum
Epitheliocystis in Seriola sp.
Importance of diagnosis
Increasingly complex
Many infectious agents ubiquitous
Cause-and-effect relationship not defined for all
Predisposing factors of greater significance?
Differential diagnosis
 Clinical history & signs
 Water quality, plankton sampling
& observations
 Fresh gill smears (on site microscopy)
 Histopathology
 PCR, bacteriology
Treatment & control
• HAB & zooplankton: stop feeding,
aerate/oxygenate?, move pens?,
enclose pens ? but early warning
required.
• Biofouling?
• AGD: freshwater baths,
hydrogen peroxide,
improve environment
• Bacterial gill disease: improve environment, antibiotic?
Monitoring
• Daily secchi disc (and
phytoplankton)
• Zooplankton
• Gross gill scores
• Histopathology
• Gross gill scores
• Fresh gill smears
Surveillance via RT-PCR
• Gill amoebae
• Microsporidians
Summary
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Gill disease highly significant health challenge
May be uni- or multifactorial
Accurate, early diagnosis crucial
Monitoring, gill disease can be progressive
Treatments available for some conditions
Improve rearing conditions
Much research required
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