What is prawn culture and rearing of Prawns

Prawn 

The class Crustacea, of which prawns are a member, is often regarded as a fish. However, it is not a fish; rather, it is an economically significant aquatic Crustacea. The prawn is an excellent source of protein and makes up a highly nutritious diet for people. It is highly prized as a culinary item all over the world because of its pleasant flavour.

Prawn Culture

Prawn larvae are typically permitted to enter the various types of culture fields, where they can be raised and harvested for marketing. And this is the culture of the prawn, according to this system.

Biology

The giant freshwater prawn are also known as Macrobrachium rosenbergii, is a native of the Indo-Pacific and northern Australian Regions. The larval stages of this species survive in brackish water following the juvenile stage, whereas the adult is found in freshwater. When mating, the male connects his spermatophore to the female's abdomen on the ventral side, and the sperm produced by the spermatophores fertilises the eggs that emerge from the female vaginal hole.

The aerated brood chamber, also known as the egg basket, is constructed of the interlocking appendixinterna of the pleopods and holds the fertilised eggs for two to three weeks. In contrast, shrimp release their fertilised eggs into the water. It takes an average of 20 days for eggs to hatch into larvae at 28°C, and females can lay 80,000–100,000 eggs during a single spawning.

Larvae are quickly moved around by the female's abdominal appendages after hatching. Planktonic larvae actively swim upside down in a tail-first position while feeding on tiny planktons. The larvae mature in 15 to 20 days and undergo metamorphosis to become post larvae, which resemble small adults and typically feed near the bottom. Within one to two weeks of metamorphosis, the post larvae start to migrate upstream into freshwater rivers and soon develop the ability to swim against swiftly moving currents and to crawl over rocks in shallow waters.

NURSERIES AND HATCHERIES

Supplying both freshwater and sea water is necessary for freshwater prawn hatcheries; the latter can be obtained from regions with salinities of 30 to 35 ppt. The salinity, pH, and dissolved oxygen levels of brackish water, which is made from brine, saltwater, or artificial sea salts combined with freshwater, should be 12 to 16 parts per trillion, respectively.

The following facilities should also be available at the prawn farm site:

• A reliable power source to guarantee essential hatchery components, such as aeration, water flow, etc., can operate without interruption.
• A continuous road connection for arriving and leaving materials access to the unbroken supplies of fresh and salt water.

• A farm shouldn't be located close to industrial areas, cities, mines, or other activities that might contaminate the water supply.

• The location of the farm should allow for the easy maintenance of a temperature range between 28 and 31 degrees Celsius.

• When necessary, food sources for larvae should be quickly accessible.

• Should be able to get veterinary and biological help whenever they need it.
• It ought to be close to other feeding locations for nurseries.

• For speedy sale after harvest, it must be close to the market.

OBTAINING BERRIED FEMALE PRAWNS

Females with berries have fertilised eggs in their egg basket. They can be obtained from rivers, canals, lakes, and estuaries, where they are most plentiful at the start of the rainy season. Berried females can be obtained all year round in the tropics from farm ponds containing adult animals. The weight of prawns at harvest is increased by selecting fast-growing, berried females from ponds.

Special brood holding facilities are not required in the tropics, where berried females are readily available, but indoor brood stocking facilities are required in temperate areas. Brood stock is disinfected by immersing it for 30 minutes in freshwater containing 0.2-0.5 ppm copper sulphate or 15-20 ppm formalin. Prawns should be fed at a rate of 1-3% of total biomass on a daily basis.

Berried females can be removed from the holding system and placed in tanks where the eggs hatch into first instar larvae, which can then be collected by netting. To prevent bright sunlight from reaching the larvae, the hatching tanks should be covered, and the inside of the tanks should be painted with black epoxy-resin paint.

Larval Rearing Tanks

Freshwater prawn larvae can be grown in a variety of containers, including circular flat-bottomed tanks, circular conical-bottomed plastic tanks, plastic-lined wooden tanks, rectangular concrete tanks, concrete-faced brick tanks, and earthen water jars. A good drainage system is required because water must be removed from tanks during harvesting. Mixing tanks and storage tanks are also required for preparing the brackish water for use in the hatchery. Aeration of the water is also required, which can be accomplished using PVC pipes with holes cut at one foot intervals.

Larvae should not be exposed to direct sunlight, so cover and shade 90% of the tan area. Natural light is required for larval survival, which can be provided by transparent roofs over hatcheries. Sand filters, drum screen filters, and medium filters, for example, should be simple to clean and designed to minimize water loss.

Before it can be used in rearing tanks, water must be chemically treated and physically filtered by passing through the sand bed before being transferred to another tank for treatment. To make 12 ppt brackish water, combine seawater or brine with freshwater. M.'s optimal temperature range rosenbergii is 28-31°C. Below 24-26°C, the larvae will not grow well and will take longer to reach metamorphosis.

larval feeding

Different hatcheries use a variety of feeding materials, including shrimp nauplius larvae, freshwater cladocerans, fish eggs, squid flesh, frozen adult Artemia, rotifers, fish flesh, egg custard, worms, and commercial feeds. The amount of food to be given is determined by the utilization of feed by larvae, which varies by location. The amount of feed consumed increases as the larvae grow.

Harvesting Post Larva

Post larvae can withstand the transfer from 12 ppt water to freshwater when they are about 7-8 mm long. They should, however, be acclimatized to fresh water in the larval tanks rather than being harvested from the larval tanks and transferred directly into holding tanks containing freshwater. When the majority of the larvae have metamorphosed, the water level in the tanks should be reduced to approximately 35 cm. The tank should then be gradually flushed with freshwater over a 12-hour period.  The post larvae can then be collected and transferred, or the larval tanks can be refilled with fresh water to a depth of 70 cm and the animals temporarily housed there. The best method for harvesting post larvae from larval tanks is to lower the water level and then remove them with nets.

Rearing Ponds

Furthermore, the size should be manageable. Most farms have ponds ranging in size from 0.2 to 0.6 ha. Large ponds are typically wider than 30 m in width and are frequently drained for harvesting. The average depth of water in tropical freshwater prawn ponds should be one metre, with a minimum of 0.75 m and a maximum of 1.2 m. Deeper ponds are used in colder climates to keep water temperatures stable. Pond banks, embankments, and bunds must be high enough to accommodate the highest expected water level in the pond, which should be 1-2 feet higher than the water level. Each pond's water flow must be controlled by valves, stop-logs, or plugs. The most effective way to increase dissolved oxygen levels in pond water is to use paddle wheels.

Stocking

Stocking the ponds quickly reduces competitors and predators, as they have less time to establish themselves. After metamorphosis, post larvae that are a week or two old are frequently used to stock ponds, where they remain until harvested. For Macrobrachiumrosenbergii monoculture, a stocking density of around 40,000/ha is recommended. Using larger juveniles for stocking increases both the survival rate and the average weight of the animals by up to 30%.

Feed Type

Natural pond productivity generally results in small pond production. To increase productivity, intensive farming must include supplementary feeding. Some farms claim to rely on fertilizers rather than feeding at the start of the rearing period, which promotes algal bloom and a diverse range of micro flora and fauna in ponds. Others discover that starting the rearing period with feed improves performance and is cost-effective. Commercial feeds are the most productive and dependable, but they are expensive and out of reach for most small farmers.

Harvesting Marketable Prawns

There are two harvesting methods: culling and draining. Harvesting time is determined in part by the rate of growth and in part by the size of the animals for market requirements. Culling is used to remove faster growing prawns that increase density quickly from ponds in order to harvest market-sized animals. Culling in the tropics typically begins 5-7 months after post larvae have been stocked to remove market-sized animals for sale while leaving smaller and soft-shelled animals in the pond to grow. Ponds are drained and all animals are sold after about 8-11 months. Cull harvesting involves pulling a seine net through the pond to remove market-sized animals, whereas drain harvesting involves installing a harvesting sump in front of the gate or outside the pond, where prawns will accumulate while the water is drained.

Diseases Controls

Several diseases affect both freshwater prawn larvae and adults. Formalin at a rate of 200 ppm daily is used in some hatcheries as an effective treatment for protozoan and hydrozoan parasites, as well as fungal diseases. Formalin can also be used at a lower concentration of about 30 ppm for longer periods of time, followed by a 24-hour water change. To get rid of diseases and parasites, larvae can also be transferred to disinfecting tanks every 5-10 days. Treatment has also included dipping larvae in Malachite green (0.2 ppm) for 30 minutes every day. It is also recommended to soak for 6 hours in a copper sulphate 0.4 ppm solution. To control filamentous bacteria, antibiotics and sulfa drugs are sometimes used, and some hatcheries use lime (CaO) as a preventative measure.

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