gill health in finfish aquaculture dr. hamish...
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Gill Health in Finfish Aquaculture
Dr. Hamish Rodger
Gill Health in Finfish Aquaculture
Outline
Gill disease background
Aetiologies of gill disease
Pathologies
Control & treatments
• 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
Main gill functions
• 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
Gill disorders – finfish farms
Causes of gill disorders
Gill Health in Finfish Aquaculture
• 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
Gill Health in Finfish AquacultureCauses of gill disease
© H. Rodger
Primary insult to gills
(phytoplankton,
zooplankton, others)
Change in environmental
conditions
Infestation or infectionColonisation of gills by
harmful bacteria
Infestation by protozoans
(costia, trichodina)
Proliferation of
parasites, other
bacteria
Direct pathology &
impact
Bacterial gill
disease/epitheliocystis/P
GI or D?
Gill disease (AGD, pox
virus, etc.)
Exposure to pathogens
0.0
5.0
10.0
15.0
20.0
25.0
30.0
% W
eekly
Mo
rtali
tySite A 08GS1 Weekly Mortality Per Pen
C1
C2
C3
C4Tenacibaculum sp. bacteria
Trichodina, marine costia, amoeba
Hyperplasia, fusion, necrosis & epitheliocystis
Gill Health in Finfish Aquaculture
Harmful algae
Gill Health in Finfish Aquaculture
Harmful algae blooms (marine)
• > 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
Photo by A. MacAteer
Fragile, bleeding gills,
inappetance, behaviour
change, visibility
Gill Health in Finfish Aquaculture
Harmful algae blooms (HAB); gross pathology
Increased mucusDiffuse necrosis,
haemorrhages
© H. Rodger © H. Rodger
Gill Health in Finfish Aquaculture
Harmful algae blooms (HAB); histopathology
© H. Rodger
Diffuse epithelial
apposition,
sloughing &
necrosis (Karenia
mikimotoi)
© H. Rodger
Gill Health in Finfish Aquaculture
Harmful jellyfish or zooplankton pathology
Gill Health in Finfish Aquaculture
What are Jellyfish?
jellyfish Little jellyfish Siphonophores Comb jellies
(Scyphomedusae) (Hydromedusae) (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
Gill Health in Finfish
AquaculturePotential vectors for pathogens?Phialella quadrata and Pelagia noctiluca: implicated as vectors of the
bacterial disease Tenacibaculum maritimum
Delannoy et al. 2011
Muggiaea atlantica© H. Rodger
© H. RODGER
Gill parasites
Gill Health in Finfish
Aquaculture
Gill Health in Finfish
AquacultureAmoebic gill disease
© H. Rodger
Neoparamoeba perurans
© H. Rodger
Gills affected with Ichthyobodo sp. & fungi (Saprolegnia sp.)
• Tenacibaculum sp. • T. maritimumBacteria
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
• Gill amoebae • Microsporidians
Surveillance via RT-PCR
• 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
Summary
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