Macrobrachium rosenbergii, also known as the giant river prawn, giant freshwater prawn, Malaysian prawn, freshwater scampi (especially in India), or cherabin, is a species of freshwater shrimp (not a prawn or scampo in terms of phylogeny, although colloquially "prawn" can refer to freshwater shrimp or true prawns) native to the Indo-Pacific region, northern Australia and Southeast Asia. This species (as well as other Macrobrachium) is commercially important for its value as a food source.^[1]

While M. rosenbergii is considered a freshwater species, the larval stage of the animal depends on brackish water.^[2] Once the individual shrimp has grown beyond the planktonic stage and become a juvenile, it will live entirely in freshwater.^[2]

Description

Grilled giant river prawns in Thai cuisine; each (whole) prawn weighing around 500 grams

M. rosenbergii can grow to a length of over 30 centimetres (12 in).^[1]

Morphotypes

There are three different morphotypes of males.^[3] The first stage is called "small male" (SM); this smallest stage has short, nearly translucent claws. If conditions allow, small males grow and metamorphose into "orange claws" (OC), which have large orange claws on their second chelipeds, which may have a length of 0.8 to 1.4 their body size.^[3] OC males later may transform into the third and final stage, the "blue claw" (BC) males. These have blue claws, and their second chelipeds may become twice as long as their body.^[2][3]

Male M. rosenbergii have a strict hierarchy: the territorial BC males dominate the OCs, which in turn dominate the SMs.^[3] The presence of BC males inhibts the growth of SMs and delays the metamorphosis of OCs into BCs; an OC will keep growing until it is larger than the largest BC male in its neighbourhood before transforming.^[3] All three male stages are sexually active, and females who have undergone their pre-mating moult will co-operate with any male to reproduce. BC males protect the female until their shell has hardened; OCs and SMs show no such behaviour.^[3]

Life cycle

In mating, the male deposits spermatophores on the underside of the female's thorax, between the walking legs. The female then extrudes eggs, which pass through the spermatophores. The female carries the fertilised eggs with her until they hatch; the time may vary, but is generally less than three weeks. Females lay 10,000–50,000 eggs up to five times per year.^[2]

From these eggs hatch zoeae, the first larval stage of crustaceans. They go through several larval stages before metamorphosing into postlarvae, at which stage they are 0.28–0.39 inch (7.1–9.9 mm) long and resemble adults.^[2] This metamorphosis usually takes place about 32 to 35 days after hatching.^[2] These postlarvae then migrate back into freshwater.

See also

Crustaceans portal

• Freshwater prawn farm

References