pond-side shrimp disease recognition for farm technicians...
TRANSCRIPT
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
LEVELS OF DIAGNOSIS (Bondad-Reantaso et al. 2001)
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
Shrimp Culture Timeline: Daily monitoring and status analysis is a must!
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
Making Sense of Farm and Laboratory Data
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.
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
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.
Diagram of Shrimp HP Development from Larva to Adult
The Shrimp Hepatopancreas (histological sections)
High Lipid Storage Low Lipid Storage
SPOT THE DIFFERENCE
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
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.
Example of on-farm microscopic findings of shrimp hepatopancreas condition
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
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
Pond-side Disease Diagnosis:
2. Gill Discoloration and Shell Fouling
Animals are good groomers!
Why do crustacean gills change in color?
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?
The Crustacean Gill Structure
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!
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.
Pond-side Disease Diagnosis:
3. Water quality and environment
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.
Our standard for hygiene should be the same for shrimp
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.
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
Hydrogen sulfide – the silent killer?
Fine tuning of water quality measurements and values is very important.
Pond-side Disease Diagnosis:
4. Loose Shell/Soft Meat
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
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.
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
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
Thank you for your attention!