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Examples of shrimp disease recognition for farm technicians through Level 1 diagnostics

Celia R. Lavilla-Pitogocelia.pitogo@fulbrightmail.org

FMM/RAS/298: Strengthening capacities, policies and national action plans on prudent and responsible use of antimicrobials in fisheries Workshop 2

in cooperation with Malaysia Department of Fisheries and INFOFISH7-9 August 2017, Kuala Lumpur, Malaysia

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 PROBLEM

Farm 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 parasitisim• 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.

- A good indicator of shrimp health

Main Functions:

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

Side View Top View Ventral/Bottom View

The Shrimp Hepatopancreas (histological sections)

High Lipid Storage Low Lipid Storage

SPOT THE DIFFERENCE

Malnutrition and Parasitism

Malnourished child = food 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 shrimpo 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!)

çGranuloma

çGranulomas è

Wet Mount

èêè

Granulomas in the hepatopancreas (arrows)

Davidson’s fixed samples

Pond-side Disease Diagnosis:

2. Gill Discoloration and Shell Fouling

Celia R. Lavilla-PitogoiAqua Malaysia

Animals are good groomers!

Why do crustacean gills change in color?

When grooming stops, appearance changes!

Causes of gill discolorationo Infectious pathogens – fungus, bacteriao Exposure to harmful chemicals = polluted water sourceo Mechanical injury resulting to melanizationo Turbid water = too much sedimentso Plankton crasho Others?

The 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 Let’s grow well-groomed and healthy shrimps.o The answer is in good water quality.

Pond-side Disease Diagnosis:

3. Water quality and environment

Celia R. Lavilla-PitogoiAqua Malaysia

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 wello 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.

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

Celia R. Lavilla-PitogoiAqua Malaysia

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 CrustaceansFor large shrimpo Underfeeding o Change in quality of feedo 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 shrimpo Pathogens or abnormalities in the HP (EHP, vibrios, granulomas,

strangulations)o Malnutrition during larval rearingo Underfeeding and all other factors that affect large shrimp

Assessing Pond Problems Based on Sizes of Affected ShrimpWhat two disease events can you see in the photo?

Shrimp with full meat

Shrimp with soft meat

Assessing Pond Problems Based on Sizes of Affected Shrimp

Shrimp with full meat

Shrimp with soft meat

- Shrimp are eating- Guts are full- Muscles firm

- Shrimp not eating- Guts are empty- Muscles watery

Histology of Shrimp with Soft Meat/Loose Shell

Hepatopancreaso Absence of stored lipids (HP is pale)o Bacterial infection in HP = secondaryo EHP varying from Grade Trace to 4

Muscleso Watery o Nuclei are abnormal

Thank you for your attention!