Macrobrachium rosenbergii, commonly known as the giant freshwater prawn or giant river prawn, is a decapod crustacean. It is one of the largest freshwater prawns globally. This species is notable for its biological features and economic importance, especially in aquaculture.
Physical Characteristics and Natural Habitat
The giant freshwater prawn has impressive physical attributes, capable of reaching lengths of up to 32 centimeters (approximately 12.6 inches). Its overall coloration can range from a bluish-green to brownish, sometimes displaying orange stripes. A distinguishing feature is the pronounced sexual dimorphism in its second pair of walking legs, which develop into large, elongated claws (chelae). Dominant males exhibit large, vibrant blue claws that can be longer than their body, indicating their status.
This species is indigenous to tropical and subtropical waters, primarily across Southeast Asia. Its natural habitats include slow-moving freshwater environments such as rivers, lakes, ponds, ditches, and canals. They are also found in low-lying floodplains and river mouths. The native geographic range extends across countries including India, Bangladesh, Myanmar, Thailand, Malaysia, Indonesia, the Philippines, and Vietnam.
Complex Life Cycle and Social Structure
The life cycle of Macrobrachium rosenbergii involves migration between freshwater and brackish environments. Female prawns carry their eggs externally until they hatch in freshwater. The newly hatched larvae require brackish water for development. Larvae drift downstream, often reaching estuarine areas where the salinity is suitable for their growth and metamorphosis.
After several developmental stages, larvae transform into post-larvae or juveniles. They then migrate upstream into freshwater habitats to mature into adults.
The social structure within male Macrobrachium rosenbergii populations is complex, characterized by three distinct morphotypes: Blue Claw (BC), Orange Claw (OC), and Small Male (SM). Blue Claw males are the largest and most dominant. They are highly territorial and engage in complex breeding behaviors and court females. Orange Claw males are of medium size with orange-colored claws and are considered opportunistic, often acting as satellite males that will eventually grow into the Blue Claw morphotype. The Small Males are the smallest, with transparent, spineless claws, and employ a cryptic mating strategy, often mimicking females to gain access to receptive individuals.
Global Significance in Aquaculture
Macrobrachium rosenbergii holds global significance in aquaculture due to its desirable characteristics for food production. It is highly valued for its rapid growth rate, large size, and high consumer demand for its delicate flavor and texture. These attributes make it a popular choice for cultivation worldwide.
Farming methods commonly involve culturing these prawns in earthen ponds, allowing for efficient production. The species’ ability to tolerate moderate changes in temperature and salinity supports its widespread cultivation. While native to Southeast Asia, Macrobrachium rosenbergii has been introduced and is now commercially farmed in numerous countries outside its original range, including Hawaii, Honduras, Mauritius, Taiwan, Costa Rica, Israel, and Mexico. This expansion highlights its economic impact as a farmed aquatic product globally.
Considerations for Aquarium Keeping
Keeping Macrobrachium rosenbergii in an aquarium requires specific considerations due to their size and behavior. A sufficiently large tank is necessary, with a minimum of 75 to 100 gallons recommended for a single adult prawn. Maintaining stable water parameters is important, including a tropical temperature range of 24-30°C (75-86°F) and a pH level between 7.5 and 8.5. As omnivores, their diet should consist of commercial sinking pellets, fresh vegetables like zucchini, and protein sources such as brine shrimp or bloodworms, offered two to three times daily.
These prawns are known for their territorial and aggressive nature, particularly the males, which can be combative towards other prawns and tank mates. They are nocturnal and hide during the day, foraging for food at night. Due to their aggressive tendencies, Macrobrachium rosenbergii is unsuitable for most community aquarium setups. They are best kept alone, or, if tank mates are considered, they should be robust, fast-moving, and non-bottom dwelling fish that can avoid potential conflicts.