P. indicus is non-burrowing, active at both day and night, and prefers a sandy mud bottom. Adults are normally found at depths less than 30 m but have also been caught from 90 m. The shrimp mature and breed mostly in marine habitats and spend the juvenile and sub-adult stages of 30 to 120 mm total length (TL) in coastal estuaries, backwaters or lagoons. Juveniles can tolerate a much wider range of salinity (5-40 per cent) than adults. On the southwest coast of India the juveniles support a good commercial fishery in the backwaters and paddy fields.
Geographic variations in size at first maturity are evident and vary from 130 to 149 mm TL. P. indicus females are highly fecund, ranging from 68 000 to 1 254 200 eggs from females of 140-200 mm TL. There are five stages in ovarian maturation: immature, early maturing, late maturing, mature and spent. P. indicus belongs to the closed thelycum group and mating takes place immediately after the females moult. During mating, which normally occurs at night, the sperm packs (spermatheca) are deposited by the hard-shelled male into the thelycum of the newly moulted, soft-shelled female. The females carry the spermatheca during ovarian maturation and the sperms are dispensed at the time of spawning.
Fertilization is external as the ripe ova released by the female become fertilized by the sperm extruding simultaneously from the stored spermatheca in the thelycum. Depending upon the temperature, hatching takes place within 8-12 hours after spawning. The nauplii are free swimming and non-feeding and pass through six moults. The larvae further pass through protozoea (3 stages), mysis (3 stages), and then to postlarvae, which resemble the adult shrimp. The postlarvae migrate into the estuaries, settle and feed on benthic detritus, polychaete worms and small crustaceans, and remain there until they attain 110-120 mm TL. These sub-adults then return to the sea and get recruited into the fishery.
Production
Production cycle
Indian white prawn production cycle
Production Systems
Seed supply
In the traditional paddy-cum-filtration systems, juveniles congregating around the sluice gate are allowed to enter into the extensive fields during high tide. Earlier, wild seeds were also caught and sold to shrimp farmers. However, with the establishment of hatcheries and also due to overfishing, the dependence on wild seeds has been reduced.
Broodstock
Shrimp spawners for breeding purposes can be sourced either from the shrimp fishing grounds or can be developed in captivity by induced maturation of the adult specimens brought from the wild (>145 mm TL) and maintained in broodstock holding tanks. When wild spawners are used, they are carefully transported to the hatchery and maintained in flow-through systems in order to recover from the stress. The females are transferred individually in 500-1 000 litre cylindroconical fibreglass reinforced tanks containing microfiltered and sterilized seawater of 30-35 ‰ salinity and at pH 8.0-8.2. A temperature range of 27-31 ºC is ideal for spawning, which takes place during the night, following which the spawners are removed and transferred to rematuration tanks.
The size of P. indicus used for broodstock development should preferably be above 145 mm TL (20 g) for females and 140 mm (17 g) for males. The specimens, after a prophylactic treatment with 100 ppm formalin for 30 minutes, are stocked at 4/m³ and at a sex ratio of 1:1 in 100 tonnes circular tanks with an in situ biological filter. The tanks are covered and kept in a dark room. Three tanks of the above size can meet the broodstock requirements of a hatchery of 18 million capacity. Shrimp are fed with intertidal oligochaetes and clam and squid meat daily. Female eyestalks are unilaterally ablated by an electrocautery apparatus for endocrine stimulation.
Shrimp mature within 9-27 days after ablation and the interval between two consecutive spawnings may be 3-15 days. P. indicus also mature and spawn in captivity without eyestalk ablation by maintaining the pH between 8.0 and 8.2, light intensity below 500 lux and feeding with oligochaetes and fresh clam meat. However, ablated females produce ten, eight and six times as many spawns, eggs and nauplii, respectively, compared to unablated females.
Estimates of the total number of eggs spawned are made by sampling. The eggs are allowed to hatch in the same tank. After estimating the total number of nauplii hatched, they are collected, washed and stocked into larval rearing tanks. Small-scale hatcheries purchase the nauplii from nauplii producing centres for further rearing to postlarvae because broodstock maturation facilities require higher investments and infrastructure. Traders pack nauplii at a density of 20 000/litre; the technology to pack at a higher density of 100 000/litre has also been developed.
Hatchery production
Smaller indoor tanks of 2-5 tonnes capacity are used for rearing larvae up to PL3-5. Nauplii are stocked at 75-100/litre and fed on a mixed culture of diatoms dominated by Chaetoceros spp. or Skeletonema spp. The concentration of diatoms in the larval rearing tanks is always maintained above 20 000 cells/ml. From second or third mysis stage onwards, larvae are also fed on an egg-prawn-custard mixture with a 100-150 µ particle size, Artemia nauplii or microparticulate feeds. Larval rearing trials without the inclusion of the expensive Artemia nauplii have been successful but higher survival is achieved when Artemia is fed.
Nursery
The postlarvae (PL5) from each larval rearing tank are transferred into a nursery tank of 10 tonnes capacity for further rearing to PL20. From PL5 onwards, artificial diets are commonly used to reduce water quality deterioration. At a stocking density of 75 nauplii/litre, survival is estimated to be 75 percent from nauplii to PL5 and 80 percent from PL5 to PL20. Twelve larval cycles can be obtained in 8 months. PL20 postlarvae can be directly stocked into grow-out ponds for farming.
Ongrowing techniques
The culture practices followed are traditional, extensive, modified extensive, semi-intensive or intensive. Traditional farming practices are still practiced in tidal ponds along the Southwest coast of India. Commercial semi-intensive farming has been adopted in Middle Eastern and in the Gulf countries. Semi-intensive farming of P. indicus in some parts of India has been replaced by P. monodon, due to higher economic returns.
Traditional
This system of shrimp farming, which involves the trapping and holding of juvenile shrimp brought in by tidal water, is practiced in Bangladesh, India, Indonesia, Myanmar, the Philippines and Vietnam. On the southwest coast of India, paddy fields ranging in size from 0.5 to 10 ha that are subject to tidal influence are auto-stocked with wild seeds of mixed varieties of shrimp and fish during November to April. These fields are seasonally used for a single crop of paddy during the monsoon season (June- September). Very large fields with deeper areas ranging in size from 2 to 75 ha, where paddy cultivation is impossible, are also used for shrimp filtration throughout the year. Shrimp feed on natural food in the ponds and shrimp production varies from 400 to 900 kg/ha/yr. P. Indicus forms 36-43 percent of the total yield of shrimp.
Modified extensive
Ponds of 1 to 2 ha in size are constructed with separate inlet and outlet facilities on elevated sites to allow complete pond drainage. Ponds are fertilized with organic and inorganic fertilizers and seeds are stocked at the rate of 60 000-100 000/ha. The shrimp feed on natural foods enhanced by pond fertilization, and supplemented by artificial diets. Water exchange of 10-15 percent is carried out daily. A production of 1 000 to 2 500 kg/ha/crop is achieved in 3-4 months of culture.
Semi-intensive
Semi-intensive ponds are stocked with hatchery produced seeds at the rate of 20-25 PL/m². Water exchange is regularly carried out by pumping. 4-6 aerators/ha are used for maintaining desired levels of dissolved oxygen. Production levels of 2 500 to 5 000 kg/ha/crop are achieved.
Intensive
Intensive farming of P. indicus was first introduced when commercial shrimp farming was initiated in the late 1980s. The adopted stocking density was 50-100 PL/m². Feeding with artificial diets was carried out 4-5 times/day. Heavy aeration and water exchange to minimize environment deterioration was practiced. The production level achieved varied from 10 000 to 20 000 kg/ha/yr, while one entrepreneur claimed a production of 12 000 kg/ha/crop on the Southeast coast of India, This farming system is not in practice in India now. However, intensive systems are used in Saudi Arabia; a private company there has reported a production of 13 500 tonnes of P. indicus from a total pond area of 2 800 ha.
Feed supply
In India farmers use locally manufactured commercial shrimp feeds (not specifically designed for this species) as well as imported feeds designed for Penaeus monodon. Some farmers prepare their own feeds but these are qualitatively poor. The cost of imported feeds is generally higher. In Saudi Arabia, the National Prawn Company prepares feeds specifically for Penaeus indicus as it is exclusively culturing this species.
Harvesting techniques
In traditional farming, harvesting starts 2 months after stocking and is carried out from dusk to dawn for 7-8 days around every full moon and new moon period. Close-meshed conical nets are fitted to the sluice gates during low tide to harvest the stock. Final harvesting from extensive farming is carried out after 3-4 months of ongrowing. Water is drained out during low tide and further reduced by pumping, using mobile diesel-powered equipment. The remaining shrimp are harvested by cast netting. In modified extensive systems and semi-intensive systems, harvesting is carried out by complete draining of the pond, the shrimp escaping through the sluice gate being collected by bag nets. The remaining stock is harvested by hand picking. In Saudi Arabia, mechanical harvesting techniques are employed.
Handling and processing
Shrimp are washed, cleaned and weighed immediately after harvesting, before transfer to ice water at 0 ºC. The rectangular crates in which they are placed are then transported to the processing plants by insulated trucks. In the processing plants, the shrimp are cleaned and sorted into various grades to suit export requirements. Depending on market requirements, shrimp may be processed into several forms, such as simple block frozen, ready-to-eat, whole chilled, IQF, and cooked products, which are exported by container ship or air cargo. As part of the worldwide marketing strategy, major processors and exporters have adopted HACCP and ISO quality control systems.
Production costs
Production costs depend upon the site, the type of culture system, the scale of production, the number of production cycles per year, and the incidence of diseases, etc. The average seed production cost in India in 2000 was estimated to be about US$ 1.6/1 000. The cost of adult shrimp produced in a modified extensive system was estimated in 1996 to be US$ 4.20/kg but, as this species is no longer commercially reared in India (only extensively), no modern cost estimates are available. The production costs for this species, as reared in Saudi Arabia, are not available.
April 2009
