|Macrobrachium rosenbergii |
De Man, 1879
Macrobrachium rosenbergii, also known as the giant river prawn, the giant freshwater prawn, the Malaysian prawn, freshwater scampi (especially in India), or the 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 and northern Australia. This species (as well as other Macrobrachium) is commercially important for its value as a food source.
While this species is considered a freshwater one, the larval stage of the animal depends on brackish water. Once the individual shrimp has grown beyond the planktonic stage and become a juvenile, it will live entirely in freshwater.
This species of shrimp can get quite large, attaining a length of over 30 cm (12 inches) .
Males can reach a body size of 32 cm;females grow to 25 cm. 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 fertilized eggs with her until they hatch; the time may vary, but is generally less than three weeks. A large female may lay up to 100,000 eggs.
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 about 8 mm long and have all the characteristics of adults. This metamorphosis usually takes place about 32 to 35 days after hatching. These postlarvae then migrate back into freshwater.
There are three different morphotypes of males. 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. 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.
Male M. rosenbergii have a strict hierarchy: the territorial BC males dominate the OCs, which in turn dominate the SMs. 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. All three male stages are sexually active though, and females who have undergone their pre-mating molt will cooperate with any male to reproduce. BC males protect the female until their shell has hardened, OCs and SMs show no such behavior.
The shrimp can be successfully raised in outdoor ponds and is readily available for sale on the Internet. Amateur cultivation of this species is particularly popular in the Midwestern region of the United States.