Farming of the Pacific white shrimp, Litopenaeus vannamei in India
Production and economics
The average productivity of L. vannamei in India during 2013 is 6.49 MT/ha/year compared to 10.3 MT during 2011. Earlier, farmers were eager to stock more (60 – 80/m2), which resulted in overproduction by a fall pricing. Farmers also faced some production problems. Thus ultimately could have led the stakeholders to resort stock reducing densities that resulted in reduced productivity during 2013. The average cost of production works out around RS 190 – 200/kg for 40 count L. vannamei producing.
The standard methods used for pond preparation in shrimp farming can be adopted depending on the soil type (eg. acid sulphate soil), weather, etc. Newly constructed ponds do not require any drying but proper bottom leveling is important. Grasses and shrubs remaining at the bottom are removed before filling water. The soil pH is checked and if it is below 7.5, lime is applied. In old ponds, bottom waste is flushed our after harvest with long hosepipes by using jet pumps. Then the bottom soil is sun dried till crack appear.
The pond bottom is scrapped using disc plough to remove the black soil. Ploughing and drying (3 times) require about a fortnight from the day of harvest. Crab fencing and bird netting are done before pumping water to prevent the auto entrance. Soil probiotics are used as a basal practice to enhance the pond soil fertility. Water in pumped in with 2 filtrations (mesh 60/square inch) each at source and pond inlet and a water depth of 1.5 meter is maintained. Water is allowed for sedimentation for 3-4 days and disinfected by bleaching at 30-50 ppm chlorine.
Development good phytoplankton bloom and maintaining it throughout the crop period is one of the most important steps towards successful crop. This helps in stabilizing the whole pond ecosystem by minimizing fluctuations in water quality.
Organic manures and inorganic fertilizers are used depending upon soil quality (fertility) to enable water regarding phytoplankton bloom development. Some farmers use organic manures such as cow dung in L. vannamei farms. They used pretreated, sundried cow dung 3 – 5 times during the culture period. Most of the farmers use organic matter derived from plant products such as deoiled rice bran and deoiled cakes (neem, ground nuts, or gingelly) and molasses as nutrient source after fermenting with yeast. A low dose (5 to 10 kg per hectare per week) of fermented organic matter is used up to 30 days of culture after seed stocking in sandy regions receiving seawater (has low organic matter). Farms receiving creek water rich in organic matter and located in clay soil do not require much organic fertilizers. In such cases, one or two doses of fermented organic matter at 5 kg/ha/week would be proper in addition to maintain the bloom. Maximum care is needed in the use of organic fertilizers. Inorganic fertilizers, such as urea (46%N) and compound fertilizers like ammonium phosphate (16:20:0) are also used at 20-30 kg/ha. After fertilization, the plankton bloom is developed within 4 – 7 days.
Stocking with SPF postlarvae
The ponds are stocked with SPF postlarvae (PL 9 -12) at the rate of 30 – 60 Nos/m2. In some parts of Tamil Nadu, farmers prefer to stock very low densities (10/m2). The farmers are allowed by Coastal Aquaculture Authority (CAA) to stock up to 60/m2. The seeds are checked for the routine health assessments and few farmers prefer PCR.
The seeds packed in oxygenated double-layered polythene bags are brought to farm site and kept in the pond water with proper acclimatization. Then the pond water was slowly added into the seed bags and subsequently the seeds were released slowly into the ponds.
L. vannamei is tolerant to wide ranges of salinity and temperature. Zero water exchange is followed up to 60 – 80 days. In areas with water seepage problems, only water addition is done. Depending on stocking density and quality water is exchanged to a minimum required level (say 10%) in some farms. Water exchange is done using chlorinated water from reservoir ponds. On an average, one HP paddle wheel aerator is used to support a production of 400 – 500 kg of shrimp. A depth of 1.25 to 1.5 meter is ideal. Optimum Water Quality Conditions for L. vannamei is given in Table 3.
|Table 3: Water quality parameters for L. vannamei culture|
12 – 20 ppt
28 – 30 oC
> 4 (mg/L)
7.7 – 8.3
30 – 45 (cm)
80 – 120 ppm
Farmers in India are comfortable with L. vannamei culture as they face less problems compared to P. monodon. Early mortalities were reported from some of the states like Tamil Nadu, which is suspected to be EMS (Early Mortality Syndrome) but this requires detailed study. Unlike P. monodon, juveniles affected with muscle cramps are not recovered. No WSSV (White Spot Syndrome Virus) has been reported from hatchery-reared postlarvae. But occurrence of White Spot Disease from ponds (horizontal contamination) was reported in some farms from Andhra Pradesh and Tamil Nadu.
Source: Asian Aquaculture Network Magazine – January/March 2014