Article: William R. More
More & More Consulting Services, Inc.
PMB 647
15600 N.E. 8th, Suite B-1
Bellevue, Washington 98008 USA
E-mail: wrmore@attbi.com

Paul Frelier, Ph.D.
Mariscos Veterinary Services, Inc.
Heyburn, Idaho

Article copied from: Global Aquaculture Advocate
October 2002, Pg.24-26

Development, Implementation of Health Programs Require Integrated Effort

Shrimp health management is generally a holistic activity in which the focus is on disease prevention through good nutrition, sound pond management, and stress reduction rather than disease treatment. Shrimp health is strongly influenced by environmental conditions in the culture environment and physical, chemical and biological factors that contribute to the growth, health and production of farmed shrimp.

Environment and Shrimp Health

Shrimp health management is a function of maintaining good water and bottom soil quality through good management techniques. These include minimizing water quality fluctuation to reduce stress in shrimp, maintaining stable populations of micro algae and keeping concentrations of harmful substance low enough to not adversely affect shrimp behavior and physiology.

Water should only be exchanged when necessary and always drained from the bottom of the pond to help flush sediments accumulated near outlets. Overfeeding and the accumulations of organic matter and attendant anaerobic conditions on pond bottoms must be managed to preclude the exchange of nutrients between bottom soil and the overlying water.

Start With PL

One hundred animals from all incoming post larvae (PL) shipments from each supplier should be examined clinically and evaluated before stocking. Please visit our web site: http://www.shrimpcare.com/PostLarvaeAnalysis.shtml for Post larva (PL) Analysis information.

Clinical examination of 20 shrimp/pond from approximately 10% of the pond should be on a weekly basis. The shrimp should be randomly caught from at least two different sites in each pond. These shrimp can be the same ones used to determine the weekly pond biomass, but must be examined while they are alive.

Pond Observations

During shrimp sampling, it is wise to look for the following:

§ Plankton blooms, color of water, shrimp swimming on the surface or shoreline.
§ Dead shrimp in the pond, stressed or dead shrimp on feed trays.
§ Shrimp with empty guts, excess feed on trays.
§ Shrimp with soft shells or head, fouling on shell.
§ Flaccid shrimp, shrimp with deformities.
§ Red discolorations of shrimp appendages or uropods.
§ Dense white appearance or opaque muscles in shrimp.
§ Brown or black gills or fouling in shrimp gills.
§ Shrimp with wounds, black areas or spots.
§ Shrimp with missing or black appendages.
§ Shrimp with black shells and superficial infections, chronic localized bacteria infections ( black lesions or splinters ).
§ Shrimp with bent or cramped tails, white muscles or muscle degeneration.
§ Shrimp color and relative size of hepatopancreas.
§ Pond bottom conditions, presence of organics or other sources of contamination.

Examinations

Specific individuals should do clinical examinations in order to have consistent data. The exams determine the percentage of shrimp in the sample that are “clinically sick”. Sick shrimp have one or move of the following:

Lethargy, anorexia (empty intestinal tract), soft shells, fouled gills or black areas on the shell.
Additional clinical signs can be added to meet the needs of a particulars farm.

A general statement of the overall health of the pond should also be recorded. This would include subjective evaluation by the pond manager that includes feed consumption as indicated by the use of feeding trays, bird activity and the number of dead shrimp seen. If the farm has a survival problem and it is not known when the animals are dying, examinations of the pond bottoms at weekly intervals may be necessary. Details of sampling should always be recorded (dates, times, locations, pond conditions, etc..).

Histology

When shrimp are approximately 5gm, sample from 5-10% of the ponds should be examined histological. This should represent a random sample caught with a cast net from four different pond locations and include 10 shrimp/pond. Sampling should then be done on a monthly or bimonthly schedule.

Examinations should also be perform at harvest on all ponds. Shrimp that demonstrate any signs of clinical disease or abnormalities should be prepared for histological examination.

If dead or sick shrimp are observed during sampling, remove 10-20 each of the suspect and healthy shrimp and send them to the lab. Shrimp under 1g should be sampled as a group. Large shrimp should be examined individually. Sampled shrimp should be placed on ice and preserved as soon as possible after being removed from the pond.

Major Stressors

The main environmental and husbandry stressors that disturb the normal physiological balance of shrimp and render the animal more vulnerable to disease include:
§ Unionized ammonia and nitrate in the presence of high pH.
§ Insufficient oxygen and elevated carbon dioxide levels.
§ Extreme of rapid changes in salinity, temperature, pH, alkalinity.
§ Molting, excess handling or high density of animals.
§ Poor nutrition.
§ Presence of heavy metals, pesticides and bacterial or algal toxins.
§ Parasitism.
§ Obligate pathogens that produce disease in healthy hosts and opportunistic pathogens that produce disease in weakened hosts.

Detecting Pathogens, Disease

For shrimp farmers, the most important aspect of disease diagnosis is the ability to detect the pathogen at the earlier stage and minimize losses by treating the disease or reducing the stressors. Once the disease has been confirmed, attempts to bring it under control can begin and the efficacy of any treatment can be evaluated.

The diagnostic process involves detecting the agent responsible for the disease and its contribution to the disease incidence. Farm staff need to be trained to recognize the gross clinical signs of the disease by the observing shrimp in the ponds and by microscope. Please visit our web site: http://www.shrimpcare.com/services.shtml and look for Shrimp diseases diagnosis and pond water Analysis & for more information.

Farms should use outside laboratories to do molecular assays like dot blots, in situ hybridization and polymerase chain reaction to confirm disease. The laboratories should also be capable of histological and microbiology work.

Animal Health Management

Three basic premises for shrimp health management:

· Many disease problems can be prevented through stress management.
· Disease treatments should be made only after a clear diagnosis of causative factors.
· Spread of disease should be minimized by reasonable regulation of importations of brood stock and larvae and isolation and disinfection of affected ponds.

Management Practices

Suggested practice for managing animal health, stress and disease include:
· Evaluated and stock only healthy, disease-free post larvae from reputable hatcheries.
· Provide proper acclimation and transportation of stocked animals. Avoid unnecessary handling.
· Use proper stocking densities for the culture systems used. Do not mix species in the same pond.
· Filter the water supply to a minimum of 250µ.
· Use good-quality feed and feed management to promote efficiency and eliminate overfeeding.
· Maintain good water quality and pond bottoms.
· Use only safe and approved antibiotics, chemicals and drugs at recommended concentrations and adjust treatments to comply with national and international regulations.
· Monitor shrimp routinely for stress, disease and health problem

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