Litopenaeus vannamei is a decapod crustacean which is native to the Eastern Pacific coast from Sonora, Mexico in the North, through Central and South America as far South as Tumbes in Peru, in areas where water temperatures are normally >20°C throughout the year. Penaeus vannamei live in tropical marine habitats. It has been introduced widely around the world since the 1970s, but especially since 2000, as it has become the principle cultured shrimp species in Asia.

Litopenaeus vannamei (Boone, 1931)

Common name: Whiteleg shrimp

Colour: Coloration normally translucent white, but can change depending on substratum, feed and water turbidity.

Species identification: It has 7-10 teeth on the dorsal rostrum and 2-4 on the ventral side.

Taxonomy:

Order: Decapoda

      Suborder: Natantia

             Infraorder: Penaeidea

                  Superfamily: Penaeoidea

                          Family: Penaeidae

                                   Genus: Penaeus

                                           Species: P. vannamei

Habitat: Depth 0 to 72 m. Bottom mud. Marine (adults) and estuarine (juveniles)

Size: Maximum size 23 cm, with maximum Carapace Length of 9 cm. Maximum weight of female 120 g. Females commonly faster growing and larger than males.

Biology: Males become mature from 20 g and females from 28 g onwards at the age of 6–7 months. P. vannamei weighing 30–45 g will spawn 1,00,000–2,50,000 eggs of approximately 0.22 mm in diameter. Hatching occurs about 16 hours after spawning and fertilization. The first stage larvae, termed nauplii, swim intermittently and are positively phototactic. Nauplii do not feed, but live on their yolk reserves. The next larval stages (protozoea, mysis and early postlarvae respectively) remain planktonic for some time, eat phytoplankton and zooplankton, and are carried towards the shore by tidal currents. The postlarvae (PL) change their planktonic habit about 5 days after moulting into PL, move inshore and begin feeding on benthic detritus, worms, bivalves and crustaceans.

Shrimp health management has become the main focus of improving production and minimizing infectious diseases in shrimp ponds for the smooth development of the aquaculture industry. To accomplish this goal, we should be concerned with the quality of post larvae especially the selection of high-health post larvae shrimp, before stocking in the pond.  

Post Larvae selection is important as it will determine the performance and production of the ponds. The objective of larvae selection is to obtain the best survival and growth in the pond. There are several characteristics of good quality post larvae, and visual observation can be used in identifying good quality or healthy post-larvae for stocking.

Some of the useful criteria are given below to help farmers identify high-health post larvae:

1. Activity:     

• Place some PL (about 100 pcs) in a basin, stir the water and check.
• Healthy PL will swim against the current. Weak PL will gather at the center.

2. Size:

• • Good and healthy shrimp Larvae should be even in size.
  • PL 10 should have a total length of 10 mm.
  • The 3 stages form one spine so PL 10 has 3 to 4 spines this is the main character of larval age finding.
  • Uneven size may be due to different Stages, underfeeding, disease, poor water quality, or over-aged Post-Larvae.

3. Disease-free:

a) Check of larvae are red/pink in color - Caused by expansion of Chromophores,it indicates

b) Any chronic or acute mortality - Indicative of advanced disease stress

c) Any limb or appendage necrosis - Indicative of bacteria infection

d) Check of fouling organism, e.g Zoothamnium  - Indicative of poor water quality Overfeeding

e) Check Hepatopancreas -

Brownish – normal

Whitish – disease problem

f) WSSV should be negative        - Accepted with PCR

4. Gut:

• • Full gut indicates good health, empty gut indicates possible stress problem

5. Molting:

• • Molting problem, indicative of nutritional disorders related to sterol, phospholipids or calcium or phosphorous

6. Pigmentation:

 (a) Shape

• Finger like – healthy
• Round Shape – unhealthy

  (b)  Color

• Rust like brown/gray / dark gray – healthy
• Yellow – average
• Blue – unhealthy

7. Muscle development:

The ratio of width of gut and body depth below the gut at the 6^thsegment,

healthy PL should be 1:4 or > 4

8. Antibiotic usage:

• • With: PL shorter, fatter and darker color sometimes with the crooked body.
  • Without: PL longer, thinner and lighter color

9. Stress test:

• • Use 200 PLs for the stress test
  • Temperature – Lower temperature to 20^oC in a short period (5-10 minutes)
  • Strong healthy PL will survive no death should occur.

10. External features:

For a healthy PL, the antennal scales of head portion are closed together whereas the tail fan (uropod) is widely opened. Closed uropods are indicative of young fry not yet suitable for stocking (

11. Feeding activity:

• • Healthy PLs have a good appetite.
  • After acclimatization.
  • PLs should feed actively.
  • When feed is available, the gut should fill up after 10-15 minutes.

Lithopenaeus vannamei is highly susceptible to a number of viral pathogens. Certain viral pathogens of shrimp, notably White Spot Syndrome Virus (WSSV) and Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV), are transmitted from broodstock to postlarvae that are then stocked with the infection, increasing the likelihood of a serious profit-limiting disease outbreak. In order to eliminate the presence, the virus in the seed, Specific Pathogen Free (SPF) stock has been developed by producing a number of generations in highly biosecure facility with continued surveillance of pathogen presence.  

SPF status refers to the absence of specific pathogens from a population of shrimp. SPF shrimp are selected through a multigenerational process that includes strict quarantine and endless sampling – typically polymerase chain reaction and histopathology – for the presence of the pathogens of concern. The primary advantage to using SPF animals relates to the ability to control disease. One can expect to see other advantages over years to come, including real disease resistance, enhanced growth and stress resistance.

The specific pathogen free (SPF) Litopenaeus Vannamei has capacity to produce quality seeds with faster growth and higher survival rates for commercial farm. The status of SPF signify that the shrimps have passed through a rigorous quarantine and disease screening process that determined them to be free from specified pathogens of concern to culturists. They are repeatedly bred under controlled conditions to maintain their freedom from specific pathogens and the SPF designation itself is tested on a regular basis. Offspring of SPF shrimp are not considered SPF unless they are produced and maintained at an SPF facility.

Many farmers have been led to believe that SPF animals can solve all of their problems. For farmers thoroughly disen­chanted with the problems associated with trying to rear non-SPF P. vannamei, the success they enjoy by the shift to SPF P. vannamei has been nothing short of miraculous. However, this does not mean they can become complacent and ignore basic biosecurity rules.