Description[ edit ] Grilled giant river prawns in Thai cuisine ; each whole prawn weighing around g M. Smaller individuals may be greenish in colour and display faint vertical stripes. The rostrum is very prominent and contains 11 to 14 dorsal teeth and 8 to 11 ventral teeth. The first pair of walking legs pereiopods are elongated and very thin, ending in delicate claws chelipeds which are used as feeding appendages.
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Body usually greenish to brownish grey, sometimes more bluish, darker in larger specimens. Antennae often blue; chelipeds blue or orange. Rostrum long, normally reaching beyond antennal scale, slender and somewhat sigmoid; distal part curved somewhat upward; dorsal and ventral teeth.
Cephalon contains eyes, antennulae, antennae, mandibles, maxillulae, and maxillae. Eyes stalked, except in first larval stage. Thorax contains three pairs of maxillipeds, used as mouthparts, and five pairs of pereiopods true legs. First two pairs of pereiopods chelate; each pair of chelipeds equal in size. Second chelipeds bear numerous spinules; robust; slender; may be excessively long; mobile finger covered with dense, though rather short pubescence.
Abdomen has 6 somites, each with pair of ventral pleopods swimmerets. Swimmerets of sixth abdominal somite stiff and hard and, with the median telson, serve as the tailfan. Eleven distinct larval stages. This discovery led to larval rearing on an experimental basis. By the Hawaiian team led by Takuji Fujimura had developed mass rearing techniques for commercial-scale hatchery production of prawn postlarvae PL.
This development spawned the first commercial farms in Hawaii and elsewhere. Both Thailand and Taiwan Province of China became pioneers in modern giant river prawn culture. The introduction of broodstock, initially from Hawaii and Thailand, into non-indigenous areas around the world began in the s. The first major FAO project designed to expand the culture of this species began in in Thailand.
Since then, giant river prawn culture has developed in every continent, particularly in Asia and the Americas. Furthermore, there is considerable production of other freshwater prawn species, notably M. Habitat and biology This species lives in tropical freshwater environments influenced by adjacent brackishwater areas. It is often found in extremely turbid conditions. Gravid females migrate downstream into estuaries, where eggs hatch as free-swimming larvae in brackishwater.
Before metamorphosis into postlarvae PL , the planktonic larvae pass through several zoeal stages. After metamorphosis, PL assume a more benthic life style and begin to migrate upstream towards freshwater. Larvae swim actively tail first, ventral side uppermost. From PL onwards prawns swim forwards, dorsal side uppermost. From metamorphosis onwards prawns can also walk, not only on the sub-stratum but also over damp areas including stones by river edges, up vertical surfaces small waterfalls, weirs, etc.
Larvae mostly consume zooplankton mainly minute crustaceans , very small worms, and larval stages of other crustaceans. Postlarvae and adults are omnivorous, eating algae, aquatic plants, molluscs, aquatic insects, worms, and other crustaceans.
Males and females have different growth rates and males exhibit heterogenous individual growth HIG ; these are vitally important factors in grow-out management. Three distinct male morphotypes and a number of intermediary types exist: small male SM , orange claw males OC , and blue claw males BC. BC males have extremely long second pereiopods; those of OC males are golden coloured; SM have small, slim, almost translucent claws.
The type and behaviour of the males affects the growth rates of other prawns. The transition from rapidly growing OC to the slowly growing BC morphotype follows a "leapfrog" growth pattern. The presence of this new BC male then delays the transition of the next OC to the BC morphotype, causing it to attain a larger size following its metamorphosis. Production Production cycle of Macrobrachium rosenbergii Production systems Seed supply When required for hatchery use, female broodstock are usually obtained from grow-out ponds but also sometimes from capture fisheries.
Normally, "berried" egg-carrying females are only used once. Commercial farms in tropical regions do not normally maintain captive broodstock for breeding purposes but adults are over-wintered indoors in temperate regions in order to stock ponds with PL as early as possible in the short grow-out season. The typical male to female ratio in broodstock holding systems is BC males or OC males per 20 females, at a total stocking density of 1 prawn per 40 litres.
Within a few hours of copulation, fertilization occurs externally, as the eggs are transferred to the brood chamber beneath the abdomen. The eggs remain adhered to the female during embryonic development, which lasts about 3 weeks.
At hatching, free-swimming zoeae are produced. Eggs are orange until days before hatching, when they become grey-black. Some seed PL; juveniles is obtained from the capture fishery where M. First stage zoeae are just under 2 mm long and grow, through 11 larval stages, to almost 8 mm at metamorphosis into PL.
Individual metamorphosis can be achieved in as little as 16 days but usually takes much longer, depending on environmental conditions. Either type of hatchery may be inland or coastal. Inland hatcheries produce brackishwater by mixing freshwater with seawater transported from the coast, brine trucked from salt pans, or artificial seawater.
Some flow-through hatcheries use a "greenwater" system, which involves fertilization to encourage the growth of phytoplankton mainly Chlorella spp. Feeding systems vary widely but typically include brine shrimp Artemia salina fed several times per day at first, reducing to a single daily feed by larval stage Prepared feed usually an egg custard containing mussel or fish flesh, squid, or other ingredients is introduced at stage 3 and its feeding frequency is increased towards metamorphosis.
Some hatcheries are integrated with nursery and grow-out facilities. Nursery Although some farmers stock grow-out ponds with young PL, many either purchase larger juveniles or rear PL in their own nursery ponds before transfer to grow-out ponds.
In temperate areas with a limited grow-out season, environmentally controlled indoor nurseries are used to increase animal size before stocking outdoors as soon as temperatures become high enough. Outdoor nurseries may be stocked with newly metamorphosed PL or with juveniles from an indoor nursery. Ongrowing techniques Freshwater prawns are reared in a variety of freshwater enclosures, including tanks, irrigation ditches, cages, pens, reservoirs, and natural waters; the commonest form being earthen ponds.
Normal rearing methods comprise various combinations of the formerly used "continuous" ponds operated indefinitely, with regular cull-harvesting and restocking and "batch" single stocking, single harvesting systems; these are known as "combined systems". Most systems involve monoculture, but the polyculture of freshwater prawns with finfish and sometimes other crustaceans also occurs, particularly in China with carps.
Integration of freshwater prawn culture with crop production also occurs typically in Viet Nam. Pond stocking densities in tropical monoculture vary widely. The prawns are fed commercial or "farm-made" feeds, the latter being single or mixtures of ingredients, often extruded through mincers and either fed moist or usually after sun-drying.
Feeds with 5 percent lipid and percent protein are commonplace and an FCR of or is achieved with dry diets. Average growth rates depend on many factors, particularly the way in which male HIG is managed. Thus the way in which grow-out ponds are managed for example, the frequency of culling out large prawns, mostly males influences total productivity.
Harvesting techniques Harvesting is either total in "batch" rearing or partial in "continuous" or "combined" rearing.
Total harvesting is achieved by gravity drain-down or water removal through pumping, while seine nets are used for regularly culling larger animals. Stretched knot mesh sizes of 1. The time and frequency of harvesting depends entirely on the volume and characteristics the animal size of market demand. Handling and processing Careful handling is essential from harvesting onwards to ensure good quality products.
Freshwater prawns tend to go "mushy" if not handled and processed correctly. Firstly, it is essential to prevent prawns from becoming crushed during harvesting. Prawns sold fresh must not be kept on ice for more than 3 days. Production costs Providing production cost data is difficult, not only because the information is usually proprietary but also because it is site-specific. For example, one review of hatchery operating costs all figures were normalised to USD gave an average of USD Hatchery investment costs ranged from USD Typically, feed expenses represented at least 40 percent of total nursery production costs.
The average cost split was 30 percent feeding, 20 percent seed, 15 percent labour and 35 percent other expenses. Diseases and control measures The major disease problems affecting Macrobrachium rosenbergii generally occur because of poor intake water treatment, poor husbandry, overcrowding, poor sanitation, and non-existent or inadequate quarantine procedures.
The measures to combat these problems are referred to as improved husbandry IH in the table below, which records some of the more important diseases. In some cases antibiotics and other pharmaceuticals have been used in treatment but their inclusion in this table does not imply a recommendation. In some cases antibiotics and other pharmaceuticals have been used in treatment but their inclusion in this table does not imply an FAO recommendation.