Freshwater prawn farming

Freshwater prawn farming is a specialized form of aquaculture. Aquaculture is the practice of raising aquatic animals for human consumption. This industry focuses on producing prawns and shrimp in controlled environments.

These farms often function as small-scale family businesses. They provide a valuable food source for people around the world. Farming these creatures requires careful management of water and biology. Farmers must understand the complex life cycles of the species they raise.

The farming process follows a specific sequence of biological stages. It begins in hatcheries, which are facilities used to produce postlarvae. Postlarvae are young prawns that have reached a specific developmental stage. These young animals are moved into nurseries for acclimation. After they adjust, they are transferred into growout ponds. In these ponds, the prawns are fed until they reach a marketable size.

Farmers then harvest the prawns using two main methods. They may use batch harvesting, which involves draining the pond. Alternatively, they may use continuous operation by fishing with nets.

Most farmed freshwater prawns belong to the genus Macrobrachium. The giant river prawn, or Macrobrachium rosenbergii, is the most common species. In 2003, this species made up about two-thirds of all farmed prawns. China also farms the Oriental river prawn, known as M. nipponense. This species accounted for about one-third of the total production. India also farms a small amount of the monsoon river prawn, M. malcolmsonii. These three species represent the entirety of the global prawn farming industry.

The life cycle of the giant river prawn involves distinct environmental shifts. Adult prawns live in turbid freshwater environments. However, their larval stages, called zoeae, require brackish water to survive. Brackish water is a mixture of fresh and salty water. After hatching, the zoeae drift toward these brackish areas. They undergo several larval stages before undergoing metamorphosis. This metamorphosis turns them into 8 mm long postlarvae.

This entire transformation typically takes 32 to 35 days. Once they become postlarvae, they migrate back into freshwater.

Male giant river prawns exhibit three distinct morphotypes, or physical forms. The first stage is the small male, or SM. These males have short and nearly translucent claws. If conditions are right, they metamorphose into orange claw males, or OC. These males possess large orange claws on their second chelipeds. The OC claws can be 0.8 to 1.4 times their body size. The final stage is the blue claw male, or BC. These large males have blue claws that can be twice as long as their bodies.

These male morphotypes create a strict social hierarchy within the pond. The territorial blue claw males dominate the orange claw males. The orange claw males, in turn, dominate the small males. This hierarchy creates significant challenges for aquaculture management. The presence of blue claw males inhibits the growth of small males. It can even delay the metamorphosis of orange claw males. To manage this, farmers must use lower stocking densities. They may stock between 1 and 20 postlarvae per square metre.

High densities are avoided to prevent cannibalism.

Global production figures highlight the importance of this industry. In 2003, the total annual production was approximately 280,000 tons. China was the leading producer, contributing about 180,000 tons. India and Thailand were also major producers, with 35,000 tons each. Other significant countries include Taiwan, Bangladesh, and Vietnam. In the United States, production was much smaller, totaling about 50 tons. This industry has grown significantly since the 1960s and 1970s.

Freshwater prawn farming offers several ecological advantages over marine shrimp farming. These farms do not salinate agricultural land. Salination is the process where soil becomes too salty for plants. Additionally, these farms do not endanger mangrove forests. Because prawns are raised at lower densities, there is less concentrated waste. This reduces the danger of ponds becoming breeding places for diseases. However, the lower yield per area means income per hectare is also lower. This makes the practice ideal for low-value lands where intensification is not required.