Introduction To Prawn Aquaculture:
Today, let us get into details of Prawn Aquaculture Practices and Expenses involved in Prawn culture.
The suitable environment for a prawn to be cultivated are tropical and sub-tropical climates. Macrobrachium rosenbergii are the species which are reared most commonly by any country as this is the species which is adaptable to any kind of backwater conditions. It is omnivorous and moreover, it accepts the food which is pelleted. The waters which have low saline content are suitable for breeding the prawns. Breeding of these species normally happens in estuaries. In these days, Hatcheries for prawns are being increased and even coming up in many states.
The production of prawn of the species Macrobrachium rosenbergii has a great increase in recent years. The reason for not expanding the prawn culture further because of the unavailability prawn seed for stocking. Aquaculture in India is getting evolved day by day as an industry. This sudden growth has occurred due to the standardization of many new techniques of input and output subsystems.
- Macrobrachium rosenbergii is a species of prawns mostly found in freshwater bodies like lakes, rivers, irrigation ditches, canals and ponds etc. In the starting stages of their life cycle, this species of prawns need brackish water. Male prawns which are mature larger than the female prawns and the second chelipeds are much larger and thicker. The head of the male is larger than the female one and it also has a narrow abdomen.
- Site selection for Prawn Aquaculture:
- Availability of water which is of good quality:
- The hatchery and nursery should be located at a place where there is a good supply of fresh water. Saline water, which would be needed for the development of larvae can be transported from some other area and can be and mixed with fresh water to attain the salinity which is required. The quality of water which is taken has a great importance for the efficient hatchery operation. Quality of water is an important factor to be considered while selecting the site.
- It is preferable to locate the hatchery sites of the prawns far from the cities and industrial areas as they may pollute the water supply. However, the supply of water should be done after a detailed analysis during site selection, in order to know their physical, chemical, and biological characteristics.
- Care is needed in hatcheries that are located near areas where the use of pesticides, herbicides, and fertilizers is more. The brackish water, which is used in the hatcheries of M. rosenbergii should be 11-18 ppt with a pH level of 7.0 to 8.5. The water should also contain a minimum dissolved oxygen level of 5 ppm. High levels of heavy metals, such as mercury (Hg), lead (Pb) and zinc (Zn), should not be encouraged as these are normally caused by industrial pollution.
Read: RAS Farming Project Report.
Soil Characteristics for Prawn Aquaculture
- A mixture of clay-silt or sandy loam comprising of 60% sand and 40% silt with good water retention capacity is an ideal soil for the cultivation of prawns. You need to have sufficient soil for the construction of the pond.
- Though you give supplemental food to the freshwater prawns which are being reared in earthen ponds, they take a small source of food from the natural resources.
- Hence, it is better to choose the site in which the soil is fertile because this reduces the need and costs of fertilisation.
- The ponds of freshwater ponds should be constructed on soil, which has good water retention characteristics.
- The soils which are very sandy or the soils which include a mixture of gravel and sand, are not suitable for Prawn Aquaculture unless the water table is high and the surrounding areas are always waterlogged.
- Soils, which consist of silt or clay, or a mixture of these with a small proportion of sand, normally have good water retention characteristics. Peaty soils are not suitable. The quantity of clay should not go beyond 60% because there is a chance of soil, getting swelled when moist and cracks occur during the dry season.
Topography suitable for Prawn Aquaculture
- The farms in which the Prawn Aquaculture is taking place should be located in such a way that it is closer to their market. Hence the road access should be taken care of as it must be good for heavy trucks be able to reach the farm easily, for the delivery of supplies and the collection of the prawns which are harvested.
- Assessment should be done to check the suitability of a site from a topographical point of view and this can be done through a survey. The lands which are flat or slightly sloping are the best ones for Prawn Aquaculture to be undertaken.
- The ideal site is the one which slopes close to 3m to 100m as it allows good savings on earth movement.
- Special care should be taken to make sure that the size of the ponds and alignments allow good construction, and at the same time give better access and effective water supply and drainage.
Climatic conditions suitable for Prawn Aquaculture
- Before selecting the site, you need to study regarding temperature, rainfall, evaporation, sunlight, wind speed and direction, and relative humidity of that locality. It is better to avoid meteorological regions which are highly unstable. The sites which are prone to strong storms and winds will raise the risks of damage due to flooding and erosion. This disturbs the transport access and even the electricity supply.
- The most important factor which you need to consider while selecting the site in terms of climate is temperature. In semi-tropical areas, there is a possibility of seasonal production in which the monthly temperature of air on an average would be above 19°C and this would be for seven months of the year.
- The optimum temperature range of production, which takes place all across the year ranges between 24 and 30°C. You would get the best results if the temperature of the water is between 27 and 31°C. T
- The investigation should be done on Rainfall, the rate of evaporation, relative humidity and speed and direction of the wind.
- The losses which occur due to evaporation should be equal to or slightly less than the rain input. This is to maintain a good water balance.
- Oxygenation between water and the atmosphere can be done through mild winds. Strong winds will increase the loss of water through and may also generate wave action. This causes erosion of the banks of the pond.
- Do not choose cloudy areas as the interference of such climate with solar penetration makes it difficult to maintain a steady water temperature.
Nursery Phase of Prawn Aquaculture
- We can have either indoor or outdoor nurseries. While choosing sites for nurseries which are done indoors, you need to follow the same pattern which you have followed to choose hatcheries.
- Site selection for outdoor nursery will be the same as that of grow-out ponds.
- After the freshwater prawns are reared in the hatchery, you need to keep them until they get ready for stocking in ponds.
- Concrete tanks of 50 m3 are comfortable for holding postlarvae (PL) before the transportation of stock into ponds.
- You can use the nets that are suspended from floats in the tanks. This is done in order to raise the surface area available to the PL but this hardens the normal operations of feeding, cleaning etc.
- You can also construct indoor nurseries with concrete or fibreglass. The size of the nursery tank should be from 9 to 50 m2 with a depth of 1m. However, the shape of the nursery tank is not that important. The stocking density, which is best suited for these tanks is directly proportional to the time for which the animals are in the tank in order to get transferred to a grow-out facility.
- The use of artificial substrates is encouraged to raise the area of the surface. These artificial substrates not only provide a home for the animals, but also increase their rate of survival.
- You can also have outdoor nurseries which are very much similar to that of grow-out ponds in terms of requirements and design. These occupy an area of 350 to 2050 m2. Outdoor nurseries also use artificial substrates like in indoor nurseries in order to surface area of prawns living in them.
- Water will be exchanged at a rate of 45% to 55% when the postlarvae are in the holding tanks. This will be done for every 3 days in order to provide aeration.
Management of Water in Prawn Aquaculture:
- For the rearing of prawns, fresh water should be used. This applies to the prawns which are in the post-larvae stage to market size.
- The salinity of water should be at least 4 ppt.
- For the supply of water in hatcheries, it would be difficult to assume the absolute quality and quantity of water because here, the importance goes to the calcium level present in the water.
- It is observed that the hard water has the increased rate of growth than that in the water which is soft.
- The pH level should be approximately 8.5.
- The alkalinity should be from 25 ppm to 42 ppm.
- It is important to maintain the temperature at 28 to 30 degrees Celsius.
Hatching Process in Prawn Aquaculture:
- When you are hatching in the ponds, heated tanks are used to stock the broodstock. This should be maintained throughout the season.
- The broodstock, male to female will be stocked at a ratio of 1:4.
- These will be stocked in heated tanks at one prawn per square feet or 8 gallons of water.
- Now, the egg development will take a time span of 14 days at 84o.
- A female prawn which is 40 g in weight can produce 18,000 larvae approximately.
- For the larval period of a month, the larvae of prawn will need the brackish water, which is having a salinity level of 11-12 ppt.
- The larvae of prawn will be very small with a weight of less than 0.2g.
- These small larvae should be fed with live food which can also be called as Artemia at regular intervals of time.
Note: There would also be the availability of seawater mixtures which are very expensive and cost 28 dollars for 400 gallons of water.
- It would nearly 4-7 weeks time to develop colonies of bacteria.
- Removal of solids and monitoring Ammonia and Nitrate content is very much required for the daily maintenance.
- To have a control of stocking density in larval tanks, you can also use larval collector.
- Moreover, you must have the larvae almost of the same age (not more than 3 days apart).
- In the primary week of hatching, larvae should be stocked in small tanks which are having a high density of greater than 1000 per litre. For 10 days, these should be fed with Artemia, two times a day.
- In the secondary week, these larvae should be moved to larger tanks which are having a capacity of 400 to 1000 gallons and the density should be decreased to 40 – 100 per litre. In this stage, the larvae should get adapted to supplemented feed.
- Supplemented diet includes 1 lb of fish, 3-4 eggs. 1 teaspoon of cod liver oil and 1 teaspoon of vitamin C.
- The rate of survival of larvae will not be more than 50%.
- In a month, the harvest of post-larvae is done and the larvae which are remaining is removed and acclimated to freshwater.
Feeding Process in Prawn Aquaculture:
- A prawn should be given at least 10% of biomass on a daily basis.
- Feeding should be done based on left overfeed at the bottom of the tank.
- Feeding is the most important factor in the management of the prawn nursery.
- If the prawns are fed poorly, then there is a chance of the prawns eating each other. At the same time, if they are overfed, the quality of water will decrease which will lead to death.
Harvesting Techniques in Prawn Aquaculture:
- In Prawn Aquaculture, harvesting will be done in two ways:
- Cull harvesting
- Drain harvesting
- Cull Harvest: In order to remove the prawns which are of a market size, a net is pulled across the pond. The net can be constructed for this purpose which can be made of monofilament nylon. These can be provided with sinkers and floaters.
- Drain Harvesting:
- This completely depends on the pond design. In this method, harvesting should be done in the early morning, mainly when there is a cool temperature. Before the harvesting is done in the morning, the level of pond water can be removed partially.
Post-Harvest Handling in Prawn Aquaculture:
- If the prawns have to be sold fresh, then it is very important to keep them in a very cool temperature. The prawns should not be placed on the ice directly because this decreases the temperature of the body and causes stress which results in the death of the prawn.
- If you want the prawns to be sold within a week of harvest, then you need to freeze them immediately after the harvest. Freezing should be done at temperatures below -10°Cr; storage at -20°C is good.
Disease Management of Prawn Aquaculture:
The prawns which are cultured are prone to various diseases due to infectious factors. These are caused by viruses, fungi, bacteria and few parasites.
Monodon Baculovirus disease:
- This can be prevented by screening the post larvae before stocking the prawns in the pond.
- There is no treatment for this disease.
- The symptoms of this disease are dark colouration, poor feeding, anorexia and lethargy.
Hepatopancreatic Parvo-like Virus:
- This can be prevented by screening the post larvae before stocking the prawns by routine histology.
- There is no treatment available for this disease.
- The symptoms of this disease include a decrease in feeding, reduced growth rate, fouling of body surface.
- This disease can be prevented through careful selection of postlarvae, elimination of horizontal transmissions which include carriers, the prawns should be provided with a good quality of fresh water and with a proper nutrition.
- There is no treatment available for this.
- The symptoms of this disease are a light yellow hepatopancreas and gills.
White Spot disease:
- This disease can be prevented by proper use of feed, selecting the best quality of postlarvae, avoiding the contaminated water into the pond.
- This has no treatment available, but it can be diagnosed. This is completely based on the appearance of intranuclear hypertrophy in stained histological sections.
- The symptoms of this disease are that the prawns start swimming on the water surface. The other symptoms include white spots accompanied by reddish discolouration of the body.
- This can be prevented by maintaining a low density of stocking and feeding the prawns with a feed of high quality.
- The symptoms of this disease are prawns which are weak and have a loose thin exoskeleton.
Surface fouling diseases:
- This disease can be prevented by maintaining good sanitary conditions at the bottom of the pond.
- For treating this disease, chlorine and formalin are used for heavy infection. The water should be changed at regular intervals too.
- The symptoms of this disease would be black or brown gills due to a heavy colony of the organisms.
Financial outlay required for setting a prawna Aquafarm/ Economics of Prawn Aquaculture:
|Capital Cost||In Rs. lakhs|
|a)||Ponds construction, drainage and feed canals, etc. (20000 m 3) Rs.25/m3||4|
|b)||Lining of feeder canal||0.6|
|c)||Water inlet structure for ponds (2 Nos.)||0.45|
|d)||Water outlet structure for ponds (10 Nos.)||0.85|
|c)||Main outlet sluices (2 Nos.)||0.3|
|d)||Generator shed, workshop, and Pump House||1|
|g)||Office, laboratory and stores||2|
|i)||Drinking water storage and supply network||0.85|
|j)||Pumps (3 Nos. Mixed flow pump of 25 HP each)||2.5|
|k)||Aerators (10 Nos. 1 HP)||2|
|m)||Generators (7 nos. X 30 KVA)||4|
|n)||Lab and farm equipments`||1|
Operational Cost for the first crop:
|a)||Seed @ Rs.300/1000 Nos. For 2 lakh||3|
|b)||Feed @ Rs.40/kg for 16,000 kg||5|
|c)||Chemicals and manures for pond preparation (@ Rs.15, 000/ha)||0.85|
|d)||Fuel and electricity||1.8|
|e)||Repairs and maintenance||1|
|g)||Labour for pond preparation||0.2|
|1 Farm manager 10,000 x 4|
|1 Mechanic 5,000 x 4|
|Farm hands (2) 4,000 x 4|
|Watchman (2) 4,000 x 4|
|i)||Office expenses and Misc. Expenses||0.5|
|Total outlay for 5 Ha||35.52|
|Total outlay per Ha.
|Rs.7.1 lakh appx.|
|Gross Income||Amount in Rs|
|Sale of big size prawn (@ Rs. 175/kg for 1000 kg)||1,75,000|
|Sale of small size prawn (@ Rs. 70/- kg for 500 kg)||35,000|
Read: Raising Free Range Chickens.