L. vannamei is native of Pacific coast of Mexico and Central and South America as far south as Peru. It is mainly found on mud bottoms, down to a depth of 75 m. It is commonly known as white legged shrimp or Mexican white shrimp. It is greyish-white in color. The maximum weight of females in the wild is about 120 g. The males are smaller at 60-80g. It lives in the column and prefers clayey loam soil.

The growth at 30°C is much higher than at 25°C. The optimal range of temperature for the species is between 30 and 34°C. At 20°C growth virtually stops. It can tolerate salinity levels of 0 to 50 ppt. Growth is uniform within 10-40 ppt.

They can grow in freshwater also but the growth is slow below 10 ppt. pH range of 7 to 9 is tolerated with optimal growth at pH 8.0. Dissolved oxygen levels above 4.5 ppm are required for optimal growth. Turbid water with flocculated particles of more than 0.5 micron resulted in better growth than clean water mainly because of the presence of algae and bacteria. Ammonia -N and Nitrite - N levels should be less than 0.1 ppm and 1 ppm respectively.

L. vannamei is an omnivorous scavenger and is less aggressive and less carnivorous than P. monodon. Food intake is more during evening and night. Retention time of food in the gut is 2.2 to 5 hours. Food is digested at modest acidities of pH 5.5-7.0. Growth of L. vannamei, under confined culture conditions was similar to P monodon till they attain 20g size. Beyond that the growth rate was poor. The shrimps attained the size of 20g within a period of 100-120 days depending on the stocking density.

Culture of L. vannamei, is being taken up in many countries because of the following c characteristics: –

• 1.It grows as fast as P. monodon upto 20 g.

• It is easier to culture in very high stocking densities of upto 150/sqm due to their less aggressive nature.

• It is tolerant to wide range of salinities of 0.5 to 45 ppt .

• It is very tolerant to low temperatures of upto 15 degree centigrade.

• It requires low protein feed (20-35%).

• It is an easy to breed species and hence domestication of the species is very successful with the production of SPF stock. Commecial availability of SPF and high-health stock is an added advantage.

• Selective breeding work for the production of SPR broodstock is easier because of the short generation period and easier captive breeding.

• Higher survival rates in hatchery (50-60%).

• Has a very good market in the US, as the most preferred species with higher meat yield (66-68%)

L. vannamei is highly susceptible to a number of viral pathogens. White Spot Syndrome Virus (WSSV), Taura Syndrome Virus (TSV), Yellow Head Virus (YHV), Infectious Hypodermal Haematopoietic Necrosis Virus (IHHNV), Lymphoid Organ Vacuolization Virus (LOVV), Reo like Viruses (REO) are some of the viruses reported in the species.

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 bio-secure facility with continued surveillance of pathogen presence. Although SPF shrimp are, by definition, free of all specifically listed pathogens, SPF shrimp may be infected with a known pathogen that is not included on the SPF list of the shrimp supplier, or with an un-known pathogen that has not yet been described.

Offspring of SPF shrimp are not considered SPF unless they are produced and maintained at an SPF facility. SPF status changes with the pathogen condition of the shrimp, as well as the type of environment within which they are cultured (level of biosecurity). One of the main advantages of culturing L. vannamei is commercially available as high health animals from Specific Pathogen Free (SPF) stocks while P. monodon have very limited availability from SPF stocks.

Stocking of pathogen free post larvae alone will not guarantee a disease free culture since the pathogens could still enter the culture environment horizontally and infect shrimps during the culture. Viral pathogens still enter the culture through:

1. By persisting in the soil

2. Intake water

3. Aquatic vectors introduced through intake water, by crabs and other animals

4. Contaminated land animals and birds

5. Contaminated farm inputs

6. Contaminated farm implements

Crabs are one of the carriers of viral pathogens and providing crab fencing in shrimp farms is considered as one of the important bio-secured measure. Carriers like crabs could also move from pond to pond over land barriers. To prevent such movements fencing made of 0.5 m plastic sheet should be put around culture pond.

Birds such as crow/ water crow pick up the dead and moribund shrimps affected with viral disease from ponds and may drop in unaffected ponds, there by transmitting the virus mechanically. This could be avoided by using bird scares and bird fencing over the pond. Feed ingredients of aquatic origin and wet/ moist feeds could be potential source of pathogens.

Pond to pond transmission could occur through the use of farm implements and farm workers. Providing an independent set of implements for each ponds and its routine disinfection before use should be mandatory.Minimum movement of workers from pond to pond and also personal disinfection of workers may also be resorted to. Bio security requirements for L vannamei farming are

• Farm to be fenced ( including crab fencing)

• Water intake through reservoirs

• Installation of bird scare/ bird netting

• Separate implements for each pond

• Effluent Treatment System ETS) in position

• Only tested and certified seeds produced in hatcheries authorized by Coastal Aquaculture Authority (CAA) to be used

• Pelleted feed manufactured by reputed companies for L vannamei farming alone to be used for minimizing feed wastage and degradation of ecosystem

Farmers are required to maintain proper records regarding seed procurement , source, quantity , stocking density as well as the quantity of shrimp produced and sold indicating the name and address of processors.           

Technical parameters of L vanammei culture includes site selection, items of development, pre and post stocking operations, stocking density, fertilisation, feeding etc.

The margin money may be considered @ 5,10 & 15% for small, medium and large farmer respectively and 25% for companies and partnership firms.

Subsidy is available for various items like pond development, construction of new ponds, first year inputs etc. under a centrally sponsored subsidy scheme implemented by majority of the State Governments through FFDA/ BFFDA's for different categories of farmers, details of which may be obtained from concerned Fisheries Departments/NFDB/MPEDA

The following categories of borrowers are eligible to avail credit.

a) An Individual.

b) A company.

c) A Partnership firm.

d) A Co-operative society.

e) A group of shrimp/fish farmers.

Training in fish farming is being provided by the FFDA/ BFFDA's, MPEDA, CIBA to the eligible borrowers and it is essential that the borrower has prior knowledge of shrimp farming before availment of bank loan.

The details of Capital Cost and Recurring Cost have been indicated in Annexure D -II. As per annexure the capital cost for excavation of 1 ha pond works out to be Rs 6,75,500/- and the recurring cost as Rs 10,31,300/-. However, the cost is indicative and actual assessment of the cost parameters have to be done while submitting the project to the bank.

As per financial analysis shown in Annexure D-III the scheme is financially viable. The financial parameters are as follows

i) NPW @ 15% Rs: 43,54,100

ii) BCR @ 15% 1.38:1

iii) IRR > 50%

Repayment of bank loan as per Annexure D – IV is 6 years. However it can vary from 6-8 years in depending upon the location and the repayment may be made in annual instalments with moratorium on repayment of principal for the first year.

NABARD provides refinance assistance for shrimp/fish culture to commercial banks, cooperative banks and Regional Rural Banks. The rate of refinance is fixed by NABARD from time to time.

Interest rate to be charged to the ultimate borrowers would be as indicated by bank/RBI/NABARD from time to time depending on quantum of loan amount and the agency providing the loan.

Security from the ultimate beneficiaries may be obtained as per the guidelines of RBI issued from time to time

I ) Farm Design Requirements:
L.vannamei lives in the column and hence increasing the depth of the pond will help in increasing density. Generally shrimp farms which were culturing P. monodon had a water depth of about 1 mt, but it is advisable to have a depth of 1.5 to 1.8 m water column for culturing L. vannamei Since mechanical aeration is one of the major requirements for L. vannamei culture, constant circulation water is expected in the pond. This will lead to the erosion of the soil in the dyke and bottom.

To avoid this compacting of the pond bottom and the dykes is essential. In intensive culture ponds, total lining of the pond HDPE sheets is done to avoid any erosion. In high density cultures, accumulation of sludge in the bottom is a major problem and provisions of central drainage or use of sludge pumps is essential. Positioning of paddle wheel/long arm aerators should aid in bringing the sludge to the centre of the pond from where it can be removed.

Bio-security requirements like reservoir ponds, fencing, crab fencing bird fencing, and disinfection facilities are incorporated in the design. To avoid disease in most cases zero-water exchange system of farming is practiced with recirculation facilities. In such cases more than 40% of the water area in the farm is allocated for reservoirs and waste sedimentation ponds.

II Management of the farm
1 Drying and Liming
The sludge left in the pond, which might have had viral disease outbreak during the previous culture, may contain high organic load, bacteria, viral particles and DNA as well as many other viral carriers. All these should be removed to prevent the persistence of viral disease. This could be achieved by the application of quick lime (CaO) @100 ppm, followed by exposure of the pond bottom to sunlight until it dries and cracks, removal of the top soil and compacting the bottom soil

2 Water Management :
White spot virus has been reported to survive as a free-living form in water up to seven days. Direct use of creek or sea water carries the risk of introducing the virus into the system. Most of the aquatic crustaceans including the planktonic forms are reported to be carriers of WSSV virus.

A number of other aquatic organisms could be mechanical carriers because of their filter-feeder habit. There is a need to eliminate these from water before use in culture ponds. Use of filter nets I 60 micron mesh/cm2 in the delivery pipes/ inlet sluice should be strictly followed. Water should be taken in reservoir ponds and treated with calcium hypochlorite @ 30 ppm and aged up to seven days, to eliminate the viral pathogens.

Farmers should ensure that only treated water be used in the culture ponds for compensating the evaporation losses. Regular water exchange is not advised to avoid cross contamination pathogens from source water.

3. Fertilization and addition of carbon source
Culture of L. vannamei can be done under two systems - with plankton as natural feed or with bacterial floc. The fertilization schedule with urea and super phosphate is followed for plankton method while provision of carbon source in the form of molasses and dolomite is used for development of bacterial floc. The volume of bio-floc was controlled at 15 ml/ liter.

4 . Stocking:
SPF shrimp seed from a reputed hatchery can be used for stocking. PL8- PL9 is normally selected after ensuring the pathogen free status of the seed. The seed acclimatization is a very important, requirement before stocking. Temperature, salinity and pH of the transportation water should gradually brought to the level of pond water by gradual mixing of both over a period of 6-12 hours depending on the difference. Stocking densities of 40 to 60 no/m2 is preferred. Higher stock density above 60 no./m2 is not permitted

5 Feed Management:
Protein requirement varies between 25 to 40% depending on the density. Marine source protein was more effective than plant source. Lipid requirement was around 6-8% with 2% marine unsaturated fatty acids and 0.25 to 0.4% of cholesterol. Feeding rate was between 6.6 to 16% for 1 gm of shrimp which will be reduced to 2% for 15 gms shrimp.

Optimal feeding frequency was between 2 and 6 in a day with maximum percentage of feed distributed in the evening and night rations. Check trays are used to monitor the feed consumption and the feeding ration is adjusted accordingly. FCR levels of 1.1 to 1.3 are expected.

6 Maintenance of Water Quality:
Regular monitoring of water quality is very essential. Water quality parameters like temperature, salinity, pH and alkalinity are monitored on daily basis. DO levels are recorded at least 2 times a day. Other parameters like Ammonia, Nitrite, Calcium, Magnesium are monitored on weekly basis.

DO levels should be maintained above 4 ppm although and operation of paddle wheel /long arm aerators should be able to maintain the level. The number of aerators required is about 1 HP per every 300 kg of biomass. The location of the aerators should be adjusted in such way the sedimentation occurs at centre of the pond, which will aid in its easy removal.

Aerators are positioned in such a way that the sludge is accumulated in the center of the pond and from there it could be removed through central drainage or using sludge pumps. Removal of sludge from the pond bottom during culture is essential in case of high density culture. In order to aid the process, sludge settled at other places should be disturbed regularly. This is achieved through dragging of chains at the bottom at regular intervals from all the sides of the pond

7. Health Management:
Weekly monitoring of shrimps for their growth and well being is essential. L. vannameinormally grows at the rate of 0.2gms/day after the first 30 days. Weekly growth rate will range between 1.5 to 2.0 gms depending on the stocking density. At 60 nos./m2, the shrimps attain 20g size within 100-120days.

8 . Harvest and post harvest
L. vannamei is a column living shrimp and hence maximum stock can be harvested by either by cast nets or drag netting and this will help in harvesting them without much overcrowding and stress. Final harvesting by draining the water should be done within 6 hours. Compared to P. monodon, L. vannamei discolours faster in case there is any delay in icing the harvested stock. Hence the stock should be 'ice killed' immediately on harvest and stored in ice.

9. Cost of production:
The cost of production of L. vannamei in Indian conditions considering the industrial rate for electricity might work out to Rs. 100 to 120 for production levels of 8 to 10 tons per ha. The average size at harvest ranges from 18 to 22 g and the sale price is more or less same for both P. monodon and L. vannamei of similar size at Rs. 200 to 220.

10. Conclusion:
L.vannamei is a suitable species for semi-intensive culture with the availability of pathogen free seed. The major issues to be considered are bio-security and maintenance of water quality through constant monitoring. It also requires higher technical knowledge to achieve better production in sustainable manner. Strict adherence to the guidelines of CAA is a must to ensure environment protection