The Giant River Prawn, scientifically named Macrobrachium rosenbergii, is a large species of freshwater prawn native to the tropical and subtropical Indo-Pacific. It is often simply called the freshwater prawn. The species is highly valued for its size and culinary qualities, leading to its extensive cultivation across numerous countries.
Identifying Features and Unique Biology
The Giant River Prawn earns its name through its impressive size. Males can reach total lengths of up to 320 millimeters (over a foot long), and exceptional specimens can exceed 400 grams. Females are typically smaller, reaching lengths closer to 250 millimeters. These animals are characterized by a smooth carapace and a prominent, slightly upward-curving rostrum armed with numerous teeth.
The most striking feature is the second pair of walking legs, known as chelipeds, which are notably elongated and robust, especially in mature males. These large claws can be vibrant blue or deep orange, often covered in dense bristles. Males exhibit pronounced sexual dimorphism, displaying three distinct morphotypes: the small male (SM), the orange claw (OC), and the dominant blue claw (BC) male.
The territorial blue claw males use their formidable chelipeds to establish a strict social hierarchy. Females are distinguished by a wider abdomen, which accommodates fertilized eggs during incubation. The life cycle involves four main stages: egg, larva, post-larva, and adult. As a nocturnal, benthic feeder, the prawn is omnivorous, consuming plants, algae, mollusks, and worms in the wild.
Ecology and Natural Habitat Requirements
The Giant River Prawn naturally inhabits tropical and subtropical waters spanning the Indo-Pacific, from India through Southeast Asia to Northern Australia. Its natural range includes rivers, lakes, and low-lying floodplains, often near brackish water zones. The species has a unique migratory pattern known as an amphidromous lifecycle.
Amphidromy means that while adults live and grow in freshwater, their larvae must develop in brackish water. Gravid females migrate downstream toward estuaries to release their eggs, which hatch into free-swimming larvae. The planktonic larvae require a salinity of approximately 12 parts per thousand (ppt) to survive and undergo metamorphosis.
After several weeks and multiple larval stages, they transform into post-larvae (PL), which resemble miniature adults. These post-larvae assume a bottom-dwelling lifestyle and actively migrate upstream. They travel far inland to complete their growth in pure freshwater environments.
Commercial Value and Global Aquaculture
The primary significance of the Giant River Prawn lies in its substantial commercial value as a food source, often marketed as freshwater scampi or Malaysian prawn. Its meat is highly prized for its firm texture and delicate, sweet flavor, often compared to that of lobster. This culinary appeal has driven its widespread adoption into global aquaculture, where production now exceeds 200,000 tonnes annually.
Farming began in the 1960s after techniques were developed to mass-rear larvae in hatcheries. The aquaculture process is divided into the hatchery phase and the grow-out phase. Larvae are raised in controlled, brackish water tanks until they metamorphose into post-larvae, typically taking about 32 to 35 days.
The post-larvae are then transferred to freshwater ponds or recirculating aquaculture systems (RAS) for the grow-out phase. A challenge in farming is the significant variation in male growth rates, resulting from the social hierarchy established by aggressive blue claw males. To maximize yield, farmers often utilize monosex culture techniques to increase the final size and uniformity of the harvest. The prawn’s shell is also processed for industrial applications, serving as a source for compounds like chitin and chitosan.