Transcript Document
Aquaculture
Royal Veterinary College
January 2004
Jimmy Turnbull
Institute of Aquaculture - University of Stirling
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Outline of the morning
Aquaculture
Introduction
to aquatic animal health
Aquatic animal disease diagnosis and
investigation
Disease control and treatment
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What is aquaculture?
Fisheries
are a form of hunting
Aquaculture is a form of farming
Any type of aquatic animal or plant
Seaweed, mussels, shrimps, fish,
crocodiles etc
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Aquaculture
Huge
75% of population in some of SE Asia
Very
industry / source of livelihoods
diverse
Climate/Water source/Species/
Systems/Intensification
Great
opportunities to travel
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FAO 1995
Aquaculture = 23% of total aquatic prod.
Total aquatic production
Fisheries
Aquaculture
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FAO 1995
Fisheries
declining, aquaculture
fastest growing food production
sector
Aquaculture produced nearly
28 million tonnes
Aquaculture more important in
developing and LIFD countries
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FAO 1995
Global meat production
100
80
Million
tonnes
60
40
20
0
Pigs
Cattle
Chickens Aquatic
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Sheep
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Aquaculture + and Exhausted
Food production vs use of fish meal
Food
security
Low cost high quality food vs
export orientated production
Food
wild catches
safety
High quality protein and lipid vs
chemical residues
Environment
Sustainable resource vs pollution
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Size and value of aquaculture
UK
Atlantic salmon industry
120,000 tonnes/year
£300 million 1999
World
production 472,000 tonnes/year
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Example - Salmon life cylce
Sea
Fresh water
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Value of ornamentals
World
£ 4,800 to 2,000 million
UK
wholesale market
wholesale value
£13 million (1994)
UK retail value in
1990 = £203 million
1998 = £104.6 million
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Ornamental fish exporters
Other
Americas
5%
16%
Europe
16%
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Asia
63%
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Ornamental fish importers
Americas
33%
Europe
37%
Other
1st
2nd
3rd
4th
USA
Japan
Germany
UK
4%
Asia
26%
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Value of ornamentals
Fish
3rd most popular pet after dogs
and cats
35
to 40 million fish imported / year
1,000 tropical species
<20 cold water species
Fish
= 75% of airlines livestock income
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Role of vets in aquaculture
Diagnosticians
Health
management / management
Research
Training / teaching
Government animal health control
Development
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Introduction to
Aquatic Animal Health
JF Turnbull
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Why Study Aquatic disease?
Why study disease?
Accademic interest
Prevent losses
Control losses
Increase production
Increase profitability / secure livelihoods
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Costs of Poor Health
Loss of fish - mortalities
Loss of production
Loss of investor confidence
Loss of opportunity
Cost of control or prevention
Wild stock
Broodstock
Fisheries
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Health management and the system
The
health of aquatic animals is more
related to their environment and
husbandry than in terrestrial animals
Diagnosis
and control depend on an
understanding of system
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Unit of Interest
Usually
only interested in the population
Not usually interested in the individual
Individuals only important as far as they
relate to the population
Try to develop an idea of what is happening
in the whole population
What
is the population?
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Unit of Interest
Population can be :
Ponds, cage or tank
Farms
Areas of a country
A whole region
EPIDEMIOLOGY you should know
about this already
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Host/Environment/Pathogen
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Environment
What can cause stress = anything!!!!
For example :
Environment or management
Nutrition
Behaviour
Other diseases
Treatments
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Host
Very
wide range of species
Salmon and carp more different than
dog and cow
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Host
Fish - inherent defences
Normal microflora
Skin
Stomach acid and gut
Especially in the gut
Carnivore vs herbivore
Fish - immunity
Non-specific immunity
Specific immunity
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Fish Skin
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Host
Fish - Non-specific immunity
Humoral - compounds in body fluids
Circulating cells
Tissue-dwelling cells
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Host
Fish - Specific immunity
Humoral - compounds in body fluids
Circulating cells
Lymphocytes
- Antibody production
Phagocytes - Phagocytosis and APC
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Host
Normal defences are labile, subject to
Endogenous changes
Moulting
in crustaceans
Reproductive state, especially in salmonids
Skin, gut, cardiovascular, immune system
Genetics
- resistant strains not successful
Immunity
Immunomodulation
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Host
Normal defences are labile, subject to
Exogenous factors :
Nutrition
Environment
esp’ temperature
Degree days
Growth
Immune response
Inflammation
Healing - skin less affected
Growth of tumours
Physical
damage
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Pathogens
Same
range of infectious
pathogens as in mammals
viruses
bacteria
fungi
protozoa
metazoa
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Pathogen
Number of pathogens varies with :
Number of sick animals
Available nutrients
Access
Easier in aquatic environment
Terrestrial disease often in fluid
for pathogen to hosts
blood, droplets, sexual
In aquaculture systems hosts concentrated
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Pathogen
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Pathogens
Examples
WSD
EUS
Ich
Salmon
lice
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White Spot Disease (WSD)
Cause
WSSV and other factors
Massive impact
US$600 million in Thailand in 1997
Affects
all systems
Extensive to Intensive
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E.U.S. outbreaks
1972
1998
1988
1983
1972
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Aphanomyces
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invaderens
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Non-infectious Disease
Nutritional
Proportion
of nutrients e.g. Ca / P
Deficiencies e.g. hypovitaminosis or malnutrition
Excesses of nutrient e.g. hypervitaminosis
Toxic compounds e.g. rancid fats, fungal toxins etc.
Environmental
Too
much e.g. ammonia
Too little e.g. O2
Genetic/congenital
Increased susceptibility to infections
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Why deal with populations?
Lab’
experiments cannot be
generalised to the farm
Level of immune stimulation
Will differ between lab’ and farm
Field challenges may (will) differ from
experimental challenges
May be unpredictable effects
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Why deal with populations?
(continued)
Large populations have inherent and
unpredictable dynamics as a result of :
Sum of individual variation in:
Non-specific defence mechanisms
Response to stress,
Level of pre-existing immunostimulation
Inherent population effects including :
Proportion infected and
Rate of transmission
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Why deal with populations?
Without
You cannot advise on :
field trial data
The magnitude of any benefits vs costs
How to use treatment for best results
The treatment is a gamble
Improved chance of success or
Another cost with no return
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Aquatic animal disease
Diagnosis and Investigation
Jimmy Turnbull
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Diagnoses
Need to look at a range of information
signs e.g. behaviour, appearance
Production information
Laboratory information e.g.
Clinical
Fresh preparations
Bacteriology
Virology
Histology
Parasitology
& others
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Standard Growth
Curve
and
Tolerance
Standard Growth Curve & Tolerance
50
45
40
ABW (g)
35
30
25
20
15
10
5
0
1
11
21
31
41
51
61
71
81
91
101 111
121 131
141
151 161
Days of Culture
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Standard Growth Curve and Tolerance
Average Growth (AA)
35.00
30.00
ABW (g)
25.00
20.00
15.00
10.00
5.00
0.00
30
37
44
51
58
65
72
79
86
93
100
107
114
121
128
135
142
DOC
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Problems with diagnosis!
Identifying
Cannot see the animals
aquatic health is difficult
Abnormal behaviour
Mortalities
Feeding often only time to observe
Clinical signs not much use
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Problems with diagnosis!
Clinical signs / examination not very useful
Farmers may use CS to spot a problem
Cannot often use CS to diagnose a
problem
Aquatic animals limited capacity to express CS
Same CS different disease or same disease
different CS
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Diagnosis
Very
similar to terrestrial animals
Identify and determine cause of problem
Presented information - often misleading
History
PATTERN OF THE DISEASE
Species / age / No affected / Groups affected
/ Onset / Duration / Clinical signs / Previous
diseases / Treatments
General farm information
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Patterns of disease
Patterns one of the most important aspects
Should lead to useful interventions
Spread over time and geographically
Associations with :
Environmental events
Batches of seed
Batches of feed
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Patterns of disease
Sudden acute sever mortality - CAUSES?
Infectious problems - PATTERN?
Propagating
Point-source
Nutritional problems - PATTERN?
Associations with risk factors
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Significance of diagnosis
Significance
of the diagnosis
Are there other problems?
Which is the most important of the problems?
What is the underlying cause?
What is the impact of the disease
On profitability
On livelihood
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Methods to identify pathogens
All
techniques used to identify
pathogens have some very serious
practical limitations
Cannot sample a large enough
proportion of the animals
Difficult to get representative samples
Test always have limitations
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Diagnostic tests - no such thing!
There are tests to identify pathogens
BUT the presence of the pathogen is not the
same as the presence of the disease
Few tests compared to terrestrial animals
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Methods to identify pathogens
How many do you sample?
PCR
< 1g = 10+
> 1g =6 ‘ish
pls. approx’ 100
How do you obtain the fish or shrimp?
Random sample e.g. from cast net
Selected sample from sick
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Methods to identify pathogens
Test
limitations
False negatives (sensitivity)
False positives (specificity)
Best tests including PCR
95% sensitive and specific
Get 5% false negatives and 5% false
positives
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Health Control and Treatment
JF Turnbull
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Course of action
Do
nothing
May not be acceptable
Change
Kill
management!!!!!!!!!!!
fish
Loss or emergency harvest
Insurance and welfare
TREATMENT
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Management changes
May
be all that is possible
Increase oxygenation
Reduce exposure to carriers
Improve hygiene
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Cost benefit analyses
Cost of
Drug
Labour
Lost production
Withdrawal periods
Mortalities resulting from treatment
Efficacy of treatment
Political / legal and ethical
considerations
Verses benefit of treatment
Re-consider
course of action
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Cost benefit analyses 2/2
Disease problem
Diagnosis
Significance
Course of Action
1. Nothing
2. Change management
3. Kill fish
4. Treatment
Drug
Method
Cost benefit analyses
ACTION
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Treatment - general precautions
Check
fish health
Starve fish
Trial therapy
Check calculations
Mix drug adequately
Beware of stock solutions
Ensure
adequate O2
Dispose of waste carefully
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Treatment
Drug?
Method
of treatment?
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Types of treatment
Immersion
Flowing
Flush
Dip
Bath
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Immersion
Flowing
Flush
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Bath Treatment in cages
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No containment
Fish movement
Water currents
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Curtain 1/3
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Curtain 2/3
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Curtain 3/3
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Full bag 1/6
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Full bag 2/6
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Full bag 3/6
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Full bag 4/6
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Full bag 5/6
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Full bag 6/6
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Bath treatment
If
it goes wrong
Increase aeration
Dilute drug or allow fish to escape from drug
Increase volume
Increase flow
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Types of treatment
In feed
Usually antibiotics
Reduce total feed and top up if necessary
Medicated food spread throughout the day
Mixing
Surface
coating
Incorporation at mill
Volume
Time
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Types of treatment
Topical
Injection
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Thank you
http://staff.stir.ac.uk/j.f.turnbull/
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http://www.aquaculture.stir.ac.uk
These lectures and other links are
on
http://staff.stir.ac.uk/j.f.turnbull/
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