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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