Recent Shrimp Diseases and Preventive Plans

By Dr. BM Hasan, Head-Aqua sales marketing Anmol Feeds Pvt Ltd.

This year again shrimp farming is facing a great hardship. In India shrimp industry is affected by White spot disease (WSD), White faeces syndrome (WFS), Running mortality syndrome (RMS), White muscle disease (WMD), White Muscle Disease (WMD), and Enterocytozoon hepatopenaei (EHP). But the greatest crop loss happens by WSD caused by white spot syndrome virus (WSSV). It poses the greatest threat to the sustainability in shrimp farming industry world over. In many occasions shrimp culture are affected by various diseases and experienced in loss of crop or reduced the production level by various reasons.

Intensive and semi -intensive aqua farming accompanies several disease problems often due to opportunistic pathogens as evident from general aquaculture. High stocking densities, high food inputs and other organic loads stimulate the selection and proliferation of opportunistic pathogens like bacteria, virus, fungi, protozoa.
 

How disease develops?

Three factors are known to interact: environment, host and pathogen. Viruses are natural microorganisms that are present in wild animals waiting an opportunity for amplification (in susceptible animals & aquaculture facilities). Detection of infection may not cause outbreak unless there is a stress or environmental triggers.

 

How it transmit?

It is well established and proved that transmission of pathogen (SEMBV) occurs by means of:

a) Vertical - From parent to offspring 

    (brood stock → eggs → larvae → PL → juvenile → adult)

b) Horizontal -Through water by infected animals (crabs/wild shrimp/zooplankton/others)

    (brood stock/nauplii & other larval stages/post larvae/juvenile/adult)

 

Why viral disease appears?

a) Inherent to the process of domestication

b) Intensification of the production

 

How WSSV enter the production facility?

-Through infected shrimp (broodstock/nauplii/PL)

-Through wild crustaceans

-Through planktons (decapods)

-Through carriers

 

Where are the bottlenecks?

It’s a complex process-analyze critically, identify pros & cons in every production/holding units:

a)  Quarantine-Are you sure it is pathogen free (SPF) before import? How the reputation or success record of exporter? Is quarantine water treated in indoor by RAS/Ozone/UV? It retains for 1-2 years & continue PCR test as surveillance?

b) Broodstock- Is the water treated by RAS/Ozone/UV- must be at least Ozone. Do you test PCR by random? Is surveillance & BAP implemented? Inbreeding and pond reared? May cause it less immune.

c)   Maturation- Do you test PCR/histology by batch or individual? Individual is better for selection.  Is the water treated by UV/Ozone-better series of filtration? Quality of live feed? Eggs dipped in iodine?

d); Nauplii- Is the water treated by UV/Ozone or only chlorination?/Nauplii PCR-ve?Checked green vibrio/luminous bac?

e)  Larval- Is the water treated by Chlo/UV/Ozone? Or series of treatments? Post larvae PCR-ve? How the size of sample? Fry health status checked? How the score? PCR test after cold challenge? Efficient disinfection in every cycle & dry out?

f)  Nursery-If intensive nursery indoor/ RAS/ water treated? Need PCR surveillance randomly. Juvenile tested PCR-ve?

g) Growout- Quality/stress test done for fry? Size of samples-how the confidence level? History of broodstock/PL? If stress by high biomass/stocking beyond carrying capacity? Sudden environmental changes cause fluctuation of parameters? Prolonged triggers (low temp/DO) including animal health (secondary infection)? Is Eh of bottom soil <-150 mV? How 250 µ filtration works-to check during growth sampling/harvest (if any crabs/wild shrimp)? Is biosecurity/BAP practiced? Any contamination from other farms or hatcheries?

Preventive plan:

Shrimp culture tends to now be developed intensively with upgraded technology for higher and successful production. High quality brooders (SPF) is very much important to achieve successful harvest.

Biosecurity is an integrated approach-not just disinfection. It should be a life style in aquaculture. Need to adapt and overcome challenges, & keeping in mind the consequences of the business as well as global food security:

-To procure reputed SPF brood stock from 2 sources and cross them up to 3-4 generations

-Ensure good detection level (PCR) by sampling multiple tissues emphasizing brood stock

-Culminate monitoring till Brood stock source & all rearing units (links) for both vertical and horizontal aspects.

-Ozone is efficient for water treatment in Broodstock/hatchery system

-Exclude WSSV through disinfection/treatment/filtration of water

-Stress management/limited water exchange/enough aeration/BAP

Optimization of Shrimp health monitoring/close track of shrimp activity in all holding units

-Successful harvest could be achieved by integrated bio security-not restricted just to your farm or hatchery