pond-side shrimp disease recognition for farm technicians...
TRANSCRIPT
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Pond-side shrimp disease recognition for farm
technicians through Level 1 diagnostics
Dr. Celia R. [email protected]
Hilton Hotel, Guayaquil,
Ecuador
September 25-28, 2017
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LEVELS OF DIAGNOSIS (Bondad-Reantaso et al. 2001)
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Diagnostic Level 1: Associated Requirements and Responsibilities
LEVE
LACTIVITY
WORK
REQUIREMENTS RESPONSIBILITY
Technical requirements
to support activities
1 Observation of
animal and
environment
Gross clinical
examination
Knowledge of normal (feeding,
behaviour, growth) of stock.
Frequent / regular observation of
stock.
Regular, consistent record-keeping
and assistance (Levels II, III).
Maintenance of records –
including fundamental
environmental information.
Knowledge contacts for health
diagnosis
Ability to submit and/or preserve
representative specimens for
optimal diagnosis (Levels II, III).
Farm worker/manager.
Fishery extension officers.
On-site veterinary support
Local fishery biologists.
Field keys.
Farm record keeping
formats.
Equipment lists
Model clinical observation
sheets.
Pond/Site record sheets.
Preservation/transportation
guidelines for Levels II/III
diagnoses. Model job
descriptions/skill
requirements.
Asia Diagnostic Guide for
Aquatic Animal Diseases
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Shrimp Culture Timeline: Daily monitoring and status analysis is a must!
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Investigation of Problems and Mortality in Shrimp Culture
MORTALITY SHOULD NOT BE USED AS
THE ONLY INDICATOR OF A PROBLEMFarm technicians need to:
1. Know what is NORMAL.
2. Recognize and analyze
situations.
3. Find trending sampling data
4. Know optimum water
parameters; what was off during
the event?
RECORD KEEPING IS VERY
IMPORTANT.Cameron, 2000
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Making Sense of Farm and Laboratory Data
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Pond-side Disease Diagnosis:
1. Slow Growth and Wide Size Variation
The definition of slow growth is relative and is a function of
individual farm goals.
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Factors that Affect Growth of Shrimp
o Shrimp Breed• Fast-growing shrimp vs. wild, inbred, etc.; SPF, SPT or SPR
• Growth is assessed based on standard curve, ABW or ADG
• Accepted growth standard is based on company target
o Shrimp Feed• Nutritional content = how much protein, carbohydrates, vitamins, minerals, etc.
• Digestibility of ingredients like fish meal and substitutes, binders, etc.
• Freshness and storage condition = old feed, old raw materials, rancid fat components, aflatoxin, etc.
• Feeding management = number of rations, time of day, pellet size and distribution, territorial behavior of shrimp (production staff should pay close attention)
o Shrimp Environment• Causes “off-feed” behavior; shrimp doesn’t eat (comparable to dirty and smelly dining table)
• Sub-optimum environmental conditions
• High salinity = requires more energy to maintain physiological equilibrium
• If problem with environment persists, transfer to new pond; early detection important• What’s the difference between stocking density and biomass?
o Abnormality and Disease • Damage in the hepatopancreas = partial or total stoppage of HP function
• Malnutrition or parasitism
• Delayed molting or failure of molting
• Infectious (EHP, Vibrio) or non-infectious (toxins) pathogens
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The Shrimp Hepatopancreas
The shrimp HP is a delicate organ that is OPEN to outside environment
through the mouth.
It is a good indicator of shrimp health
Main Functions of the Hepatopancreas:
DIGEST food
ABSORB food
STORE food
SLOW GROWTH happens when any of the above functions is impaired.
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Diagram of Shrimp HP Development from Larva to Adult
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The Shrimp Hepatopancreas (histological sections)
High Lipid Storage Low Lipid Storage
SPOT THE DIFFERENCE
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Malnutrition and Parasitism
Malnourished child = food is not enough or not
suitable (ex. Milk is not digested; diarrhea)
Child with intestinal parasites = parasites take away food from child
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EHP is an infectious disease affecting shrimp (Parasitism)
o EHP does not directly cause mortality, but the parasite can potentially cause severe growth retardation and can affect farm production.
o Presence of parasites and severity of parasitism need to be correlated with growth performance and feed convertion ration (FCR) to be properly managed.
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Example of on-farm microscopic findings of shrimp hepatopancreas condition
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There is more to slow growth than EHP.
In this case, diagnosis by microscopy is more important than PCR.
Granulomas and strangulations in HP tubules are not caused by EHP
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Granulomas in HP
• Indicate chronic bacterial infection due to various
species of Vibrio (harveyi, parahaemolyticus, other
species)
• The presence of vibrios is associated with
accumulation of organic matter within the pond
• Direct effect of chronic vibriosis is slow growth
• Slow growth is directly proportional to degree of HP
damage and extent of granuloma formation
• Granuloma formation is a slow process
• Long-term effect is chronic mortality
• Diagnosis can be done by wet mount and microscopy
(or use your smart phone cameras!)
Granulom
a
Granulomas
Wet Mount
Granulomas in the hepatopancreas (arrows)
Davidson’s fixed samples
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Pond-side Disease Diagnosis:
2. Gill Discoloration and Shell Fouling
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Animals are good groomers!
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Why do crustacean gills change in color?
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When grooming stops, appearance changes!
Causes of gill discolorationo Infectious pathogens – fungus, bacteria
o Exposure to harmful chemicals = polluted water source
o Mechanical injury resulting to melanization
o Turbid water = too much sediments
o Plankton crash
o Others?
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The Crustacean Gill Structure
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Preening in crustaceans will get rid of fouling: presence of fouling organisms
on shell and gills indicate weak shrimp or rapid environmental deterioration.
Treat the cause and not the symptom!
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Important reminders!
o Part of the shrimp’s day-to-day activity is spent cleaning its body.
o If it is not feeling well, it will not preen or groom itself.
o Even if the shrimp grooms itself, its normal preening behavior will not be
enough if the environment is dirty.
o The energy it spends on grooming will have an effect on its growth.
o The answer is in good water quality.
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Pond-side Disease Diagnosis:
3. Water quality and environment
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Water quality and feeding scenarios in the shrimp pond
Where is
food?
I can’t
smell my
food.
My food
is not
enough.I can’t go
near the
food.
I don’t like
to eat!!!
The pellets
are too
big/small.
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Our standard for hygiene should be the same for shrimp
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Loose shell and/or soft meat are manifestations of sub-optimum feeding.
What to do?
o Check if shrimp are eating well
o Examine feed record, supply, quality, feeding frequency, etc. What change happened?• Change feed or adjust amount
• Give supplementary diet
• Supplement pellets with vitamins, minerals, etc.
o Examine water quality record• Change water to improve quality
• Apply mitigation measures like probiotics and other acceptable products
o Examine stocking density, biomass, and pond carrying capacity – thin out or do partial harvest
o When above strategies fail, HARVEST while shrimp quality is still at its best.
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EXAMPLE: Table of Water Quality Parameters
(on-farm alert system)
Parameter Standard/Optimum Value Yellow Flag Red Flag
pH AM/pH PM 6.5 – 8.5? ?
pH difference Less than 0.2 Above standard Above standard
Temperature 28 – 33 Celsius Above/below standard
DO > 4 < 4 ? Paddle wheel
aerator breakdown
H2S < 1 ppm? ?
Alkalinity 80 – 100?? ?
Nitrite? ?
Transparency Depends on culture system (ex. Biofloc method ponds would have low transparency
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Hydrogen sulfide – the silent killer?
Fine tuning of water quality measurements and values is very important.
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Pond-side Disease Diagnosis:
4. Loose Shell/Soft Meat
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It’s all about body mass and muscles!Weight loss in humans is easily seen:
• Loss of fat in specific body parts
• Loss of muscle mass
Did not eat -
anorexia
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Indicators of weight loss in crustacean
CRAB = large shell, light
weight; no muscles inside
SHRIMP = loose shell, soft meat = weight loss
After weight loss:• People can change the
size of their clothes
• Shrimps cannot reduce the
size of their shell and the
outcome is loose shell.
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Possible Causes of Weight Loss in Crustaceans
For large shrimp
o Underfeeding
o Change in quality of feed
o Shrimp stopped eating due to stress from:• Water quality and environment (high salinity, non-optimum temperature, etc.)
• Toxic factors in feed, water and environment
For small shrimp
o Pathogens or abnormalities in the HP (EHP, vibrios, granulomas, strangulations)
o Malnutrition during larval rearing
o Underfeeding and all other factors that affect large shrimp
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Assessing Pond Problems Based on Sizes of Affected Shrimp
What two disease events can you see in the photo?
Shrimp with full meat
Shrimp with soft meat
Shrimp were eating
- Guts are full
- Muscles firm
Shrimp did not eat
- Guts are empty
- Muscles watery
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Thank you for your attention!