Aquaculture production has grown enormously in recent years and among that Penaeid shrimps are one of the most important cultured species worldwide especially in Asia due to their high economic value and export .A new shrimp species Litopenaeus vannamei species introduced and culture practice has been carried out in many coastal states of India last few years. Presently it is dominated 90 % of total shrimp culture. The penaeid shrimp Litopenaeus vannamei exhibits fast growth rate and its culture period is significantly reduces compared to Penaeus monodon, thus the Litopenaeus vannamei has been established as alternative to Penaeus monodon to shrimp farming in several countries.
Shrimp Culture in West Bengal
West Bengal is considered with the largest impounded brackish water area in the country and spreading over 3 districts namely Purba Medinipur, North 24 Parganas and South 24 Pargana, of West Bengal, has 5618.22 ha of culturable brackish water area, among which 3342 ha of potential areas are suitable for shrimp farming (Upadhyaya 2001).
The Purba Medinipur district has the available of 3342.0 Ha suitable potential areas of shrimp culture and mainly these areas already developed for extensive and improved extensive culture practice with P.monodon species since few years back. Litopenaeus vannamei species has been started culture practice since year 2012 and presently vannamei species dominated around 90 % of total shrimp culture.
Pond Size & Design
Most of the ponds are situated near Kalinagar Canal and its branches as well as in & around other saline creeks. Majority of farms are of small sizes ranges from o.1 Ha – 0.3 Ha water spread area. Most of farms are not having the separate water inlet and out let systems, the maximum 2-3 ponds are in each farm zone or owned by single person. The maximum ponds are converted for shrimp culture from agricultural paddy fields. The culture practice has been carried out in year old ponds and also every year newly constructed ponds are added for culture. The shrimp farms are owned by self owner or taken on lease @ Rs.20,000/- - 30,000 /- year/ acre.
2.1 Pond Preparation
The pond bottom of newly developed and excavated pond are treated with high dose of lime powder around 400- 500 kg / one hectare areas. For culture pond after harvest, the pond bottom is allowed to dry and crack to promote the capacity of the hydrogen sulphide and to eradicate the micro or macro organisms and other predators. The scraping of pond bottom is made up to 3-4 inches and special in zone of high organic black soil areas. The scraping black soils are removed and thrown away from the pond side. Then the pond bottom is thoroughly ploughed at a depth of 30 cm to remove the obnoxious gases existing in the soil. The pond bottom is treated with lime as well as bleaching powders. For liming, farmers are used quick lime, agricultural lime and dolomite .
Pond Preparation: Pond Bottom Drying, Tilting and Liming
The saline water is entered to pond through pumping after fine filtration systems up to 3-4 ft water level. The filled water has treated with Chlorine at 20 ppm-30 ppm and left for one week. The pond water has conditioned with minerals, probiotic, yeasts, local prepared organic juice etc before stocking.
Biosecurity: Certain extent of bio security measures are carried out in some of farms like bird netting, crab fencing etc but most of farms are lack of proper biosecurity.
Stocking: The stocking of quality L. vannamei post larvae pl12 – PL16 are procured from the shrimp hatcheries after quality and PCR tests. The shrimp post larvae are transported from hatcheries to culture ponds by road and flights services. The stocking of post larvae are undertaken after proper acclimitzation process.
Stocking Density: The stocking density of shrimp post larvae in most of pond are in range of 70 -100 no /m2. Also highest stocking density of shrimp post larvae in some of ponds are above 120 to 150 no /m2.
Feeding: The all the farms used formulated commercial pellet shrimp feeds from various companies for routine feeding purposes. Maximum number of farms adopted a combination of broadcasting and check tray method as feeding strategies. Regularly the daily feeding are adjusted as per the check tray observations .Feeding frequencies mostly adopted by the maximum farms @ 4 times day and according prescribed feed chart of individual feed companies.
Water Exchange: Water level has maintained 1.0 meter to 1.3 meter throughout culture period by adding water to pond through pumping from near saline creek due to evaporation losses or seepage losses etc. Most of ponds are not able to make water exchange in regular basis due to non availability of quality saline water adjacent to their pond side. However, some extent of drainage from pond can be undertaken in case of very poor water quality or severity of shrimp health conditions.
Aeration: 1-3 no of paddle wheel aerators of 1 HP and one spiral paddle wheel aerators are fixed according farm size and stocking density in different corner of pond. The aerators are under operation around 8-12 hours per day for aeration purposes during entire culture period.
Paddle wheel aerators are provided per pond to create water current for the accumulation of wastes in the center of the pond and to increase the dissolved oxygen in the water column. Aerators are placed 10’ away from the dykes and almost 40 mt. distance from each other.
Aeration in shrimp ponds
Water & Soil Treatments: After stocking, the soil & water probiotics, Minerals, Zeolites, ammonia reducer compounds, Dissolved Oxygen (DO) enhancer compounds, water disinfectants are widely used in pond water periodically in regular intervals based on the water & soil quality and condition of shrimp health. The pond bottom sediment turns black color(Sludges) according the increases of culture days and increase rate of feeding dose. The sludge formation is controlled in pond by applying sludge digesting probiotic products from various commercial companies.
The various feed supplements are applied along with pellet feed and fed to shrimps for promotion of growth, avoiding loose or soft shell, prevents 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
Range of Water Quality Parameters: The major water parameter are measured and recorded in daily or weekly by the help of field testing instruments and test kits. The major water quality parameters like salinity, dissolved oxygen, pH, temperature and total ammonia nitrogen (TAN) are monitored in regular intervals. The major water parameters of most of ponds are in following range.
Sampling: Weekly sampling is very important to know the shrimp health, growth and survival. The first sampling has been carried out in all ponds at the 60 DOC onwards of the culture. During sampling the growth & survivals of the shrimps has varied depends on the stocking density.
Feed Check tray and Sampling by cast net
Growth & Survivals
Sampling has undertaken in the pond fortnightly during early hours of the day with cast net after 60 DOC in most of ponds. Four to five hauls are made in each pond. The individual weight of shrimp are observed and assessed the other health matters like healthiness, survivals, moults, average body weight (ABW), diseases or infections etc .
The average shrimp body growth rate are inrange 18 gm -20 gm in 90 days of culture with survivals of 70-90 %. The final shrimp production rate ranges from 12.0 ton to 24 ton/hectare depending stocking density, growth rate and % of survivals.
Harvest & Marketing: Shrimps are harvested by the drag nets in most of the ponds. The harvested shrimps are packed with ice in trays after proper washing in fresh water. The shrimps are sold according the count and size.
Shrimp Harvesting by drag net
Labour Management: In most of 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.
The most of ponds are faced various constrain and problems during culture period.
Environmental & Pond Problems: Non available of saline water in time, natural calamities such as: Floods and Cyclones, Heavy rain falls, high temperatures etc.
Shrimp Health Matters: Poor quality shrimp post larvae supplied by hatcheries, mortality in early DOC, Stunted growth, diseases like: WSSV, vibrio infections, black gill, white feces & whit gut, EHP, luminescence bacteria (LB) , filamentous algae, loose shell / soft shell etc.
Market: Low price, Non available of buyers in timely etc.
Special Features of Vannamei Shrimp Culture in Purba Medinapur
The small size earthen ponds of vannamei shrimp culture in Purba Medinapur dist., are having unique features and some extent different from other parts of countries.
- The most of earthen ponds are in small sizes and ranges in 0.1 -0.3 ha.
- The stocking density of shrimp post larvae is very high compare to other parts of culture areas. However, in some ponds stocking has been undertaken in highest 150 no/m2.
- The harvest of shrimps in most ponds is ranges 12 ton to 24 ton / Ha/ crop which is highest production level in country.
- The growth and survivals are in higher range.
- The success of culture is in range of 70-85 % in maximum ponds.
- The % waterexchange(out let) in most of ponds are zero and additional water has added to pond in time to time for maintaining minimum water level.
- The pond management and culture practice are undertaken by the farm owners and their family members with limited knowledge of advanced shrimp technology.
- The culture developed in ponds with minimum expenditure cost and gain of profits.
- The maximum expenditures are included for purchase of Shrimp seeds, Feeds, Diesel, Pond health care products, etc.
- The production, growth rate, survivals are in better level compare to the other parts of culture areas in country with considering the stocking density as well as water exchange.
Case Studies of Randomly selected Shrimp Culture Ponds(Vannamei)
The growth, survivals, body weight, total harvest etc are given in the following tables of observations from few ponds.
The average body weight ranges from 8.2 gm -10.6 gm during 62 DOC period. During harvest, the average body weight of shrimps ranges 18.8 to 23.8 gm. after 83 DOC - 97 DOC respectively. The average body growth of shrimps ranges 2.0 gm to 2.6 gm /week. The survival of shrimps in all ponds ranges from 74.8 % to 84.4 %.
Stocking Density, survivals & Weekly growth performances
Shrimp survivals as well as average body growth rate are quite well considering the dimension of the pond, stocking density and zero water exchange of shrimp culture ponds. Though presently these high stocking ponds are showing better results with low biosecurity & limited water management but more attention will be require on strict biosecurity in pond systems and best pond management practice for sustainable culture practice in future days. Also it is essential that extensive training programme to be conducted for farmers, in order to develop confidence to practice shrimp culture for maintaining the sustainability of this industry.