Management of intensive Vannamei shrimp ponds
Prakash Chandra Behera, Business Head-Aqua, PVS Group, Vijayawada, India looks at how to manage Vannamei shrimp ponds with high stocking density and no water exchange in relation to growth, survival and water quality.
Aquaculture production has grown enormously in recent years and Penaeid shrimps are one of the most important cultured species worldwide, especially in Asia, due to their high economic value and export.
Litopenaeus vannamei (whiteleg shrimp) species, which have been introduced to many coastal states of India, now account for 90 percent of the country's total shrimp culture. The species exhibits a fast growth rate and its culture period is significantly shorter than that of Penaeus monodon (tiger prawn), making it an attractive alternative to tiger prawn production in several countries.
Shrimp culture in West Bengal
West Bengal includes part of the largest impounded brackish water area in the India, spread over three districts - Purba Medinipur, North 24 Parganas and South 24 Pargana - which account for 5,612 ha of culturable brackish water.
The Purba Medinipur district has 3,342 ha suitable for shrimp culture and much of this area has already been developed for extensive and improved extensive culture practice with P. monodon. L. vannamei have been cultured here since 2012 and presently make up around 90 percent of the region's total shrimp production.
Pond size & design
Most of the ponds are situated near Kalinagar Canal and its branches as well as in and around other saline creeks. The majority of farms consist of 2-3 ponds between 0.1 ha and 0.3 ha in size and most do not have separate water inlets and outlets. Most have been converted for shrimp culture from agricultural paddy fields. Those that are leased are rented for Rs.20,000/- - 30,000 /- year/ acre.
The bottoms of the newly developed and excavated ponds are treated with high dose of lime powder, around 400-500 kg / hectare. After harvest, the pond bottom is allowed to dry to eradicate possible sources of disease. The black soils are removed, then the pond bottom is thoroughly ploughed at a depth of 30 cm to remove the noxious gases existing in the soil. The pond bottom is treated with quick lime, agricultural lime and dolomite .
Pond preparation: pond bottom drying, tilting and liming
The brackish water is pumped into the pond through fine filtration systems up to a depth of 3-4 feet. The water is treated with chlorine at 20 ppm-30 ppm and left for one week. The pond water is also treated with minerals and probiotic yeasts before stocking.
Biosecurity: certain biosecurity measures are carried out like bird netting, crab fencing etc, but most farms lack proper biosecurity.
Stocking: quality L. vannamei post-larvae pl12 – PL16 are procured from shrimp hatcheries after quality and PCR tests. The post-larvae are transported from hatcheries to culture ponds by road and air, and should only be stocked after a proper acclimatisation process.
Stocking density: The stocking density of shrimp post-larvae is usually in the range of 70-100/m2 but can be as high as 120-150/m2.
Feeding: all farms use formulated commercial pellets for routine feeding purposes. Most use a combination of broadcasting and check tray methods as feeding strategies, adjusting the levels regularly according to observations. On the whole they are fed four times a day, according to the recommendations of individual feed companies.
Water exchange: the water level is maintained at a depth of 1-1.3 m throughout culture period by pumping water into the pond from nearby creeks. Most ponds are not able to exchange their water on a regular basis due to their limited access to quality saltwater. However, some drainage from pond can be undertaken in case of very poor water quality or shrimp health conditions.
Aeration: one to three single horse power paddle wheel aerators are usually used, depending on farm size and stocking densities. The aerators typically operate for 8-12 hours per day during the entire culture period and create water current for the accumulation of wastes in the centre of the pond and to increase the dissolved oxygen in the water column. Aerators are placed 3 m away from the dykes and almost 40 m apart.
Aeration in shrimp ponds
Water & soil treatments: After stocking, probiotics, minerals, zeolites, ammonia reducer compounds, dissolved oxygen (DO) enhancer compounds and disinfectants are widely used at regular intervals. The pond bottom sediment turns blacker with the increase of culture days and rate of feeding dose. The sludge formation is controlled by applying sludge digesting probiotic products from various commercial companies.
The various feed supplements are applied along with pellet feed for the promotion of growth, avoiding loose or soft shell, prevent diseases etc.
Application of home-made juice: A homemade juice is applied once in a week. 8 kg of sugarcane jiggery, 20 kg of rice bran, 32 kg of dolomite, 200 gm of yeast powder, 500 gm of curd are mixed thoroughly in an earthen tub and soaked for 1-2 days and applied to tank water @ 30 lt/tank to keep the tank environment at optimum level.
Shrimp culture pond views
Water quality parameters: the major water parameters are measured and recorded daily or weekly with the help of field testing instruments and test kits. The major water quality parameters - salinity, dissolved oxygen, pH, temperature and total ammonia nitrogen (TAN) - are monitored at regular intervals. The major water parameters of most of ponds are in the following ranges:
Sampling: Weekly sampling is very important to assess shrimp health, growth and survival.
Feed check tray and sampling by cast net
Sampling is undertaken fortnightly at dawn, with cast net, after 60 DOC in most of ponds. Four to five hauls are made in each pond to assess survival, moulting stage, average body weight (ABW) and health.
The average growth rates are 18 gm -20 gm in 90 days of culture with survival rates of 70-90 percent. The final shrimp production rate ranges from 12 tonnes to 24 tonnes/hectare depending stocking density, growth rate and mortality levels.
Harvesting and marketing: Shrimps are harvested by drag nets in most ponds. The harvested shrimps are packed with ice in trays after proper washing in fresh water.
Shrimp harvesting by drag net
Labour management: In most ponds, the day to day activities are carried out by farm owners and their family members. In certain occasions, they hire extra manpower for harvesting, construction works etc.
Most ponds face various constraints and problems during the culture period.
Environmental and pond problems: water shortages, floods, cyclones, prolonged high temperatures etc.
Shrimp health matters: Poor quality shrimp post-larvae supplied by hatcheries, mortality in early DOC, stunted growth and diseases such as WSSV, vibrio infections, black gill, white faeces and white gut, EHP, luminescence bacteria (LB), filamentous algae, loose shell / soft shell etc.
Market: Low price, non-availability of buyers.
Special features of Vannamei shrimp culture in Purba Medinapur
The small earthen ponds of Vannamei shrimp culture in Purba Medinapur have a number of unique features.
Most earthen ponds cover only 0.1-0.3 ha.
The stocking density of shrimp post-larvae is very high compared to other culture areas - up to 150/m2.
Harvest volumes are 12-24 tonnes/ha/cycle - the highest yield in India.
The growth and survival levels are the best in the country.
Survival levels are 70-85 percent in most ponds.
Most ponds have no outlets for water and need to be topped up on a regular basis.
The farms are mainly operated by the owners and their family members with limited knowledge of advanced shrimp technology.
The main costs are the purchase of shrimp seeds, feeds, diesel and health care products.
Case studies of Vannamei shrimp culture ponds
The key statistics for five ponds selected at random are:
The average body weight ranges from 8.2 gm -10.6 gm during 62 DOC period. During harvest, the average body weight ranges from 18.8 to 23.8 g after 83 DOC - 97 DOC respectively. The growth rate ranges from 2.0 gm to 2.6 gm /week. The survival levels range from 74.8 % to 84.4 %.
Stocking density, survival and weekly growth performance
Shrimp survival and growth rates in this region are impressive considering the dimensions of the ponds, stocking densities and lack of water exchange.
However, while presently these ponds are showing better than average results despite minimal biosecurity and water management more attention will be required in the future to ensure strict biosecurity and best management practice. It is also essential that extensive training programmes are offered to farmers to maintain the sustainability of the industry.
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