Indoor freshwater shrimp farming refers to the nursery stage of prawn farming (usually Macrobrachium rosenbergii). This is the postlarval (PL) stage, from when they leave brackish water for freshwater until the older juvenile stage, when they are transferred to outdoor "grow-out" ponds.
Postlarvae weigh 6 to 9 mg (0.0002 to 0.0003 oz) and are 7 to 10 mm (9/32 to 13/32 inches) long. They can survive at much higher densities than when they reach larger size. The indoor nursery allows them to grow quickly in a protected environment, until they are large enough to handle outdoor ponds. Each batch of PL stays in the nursery from 20 to 60 days. Length of stay is determined by climate.
Tanks are usually made of concrete or fibreglass. Plastic is sometimes used but runs the risk of leaks and is harder to clean. Glass tanks are fragile and are not economical. Metal is poisonous to prawns. The inside of tanks should be dark coloured (green, blue or black) to reduce stress. Commercial tanks are generally 10 to 50 square meters (108 to 538 square feet), but the size of the tanks is not as important as density of PL. The water depth should be 1 m (40 inches). Density is based on cubic meter of tank. In a water-only tank, maximum density is 1,000 prawns per cubic meter (28 per cubic foot). Providing substrate increases the maximum density to 2,000 per cubic meter (56 per cubic foot), and is much more humane. If PL must stay in the nursery after day 20, their density should be reduced further. Water temperature is 27 to 31 degrees C (81.6 to 87.8 degrees F). Use commercial in-tank heaters and thermometers. Normal ambient daylight is sufficient.
Substrate is anything placed in the tank that the prawns can cling to. Lack of substrate causes death from stress and cannibalism. Popular substrates are branches and various forms of plastic mesh. Avoid galvanised metals (such as hardware cloth) because they are toxic to the prawns. Substrate should be placed so that it does not interfere with cleaning. If you are siphoning the bottom, you must be able to move the substrate easily.
Aeration and filtration
Aeration is necessary for survival. A backup generator is highly recommended. Filtration can be a flow-through system that constantly replaces the water but this method can be wasteful and expensive. A recirculating system with biological filters is recommended. There are two opinions on siphoning. The first recommends removing all debris from the bottom to prevent disease and maintain water quality. The second allows debris to build up and grow tiny organisms that the prawns eat to supplement their diet. Consider water quality and mortality effects to determine which system is more appropriate and economical.
In the wild, prawns feed on plant and animal matter they scavenge, and tiny organisms they catch. Captive diet is pelleted prawn or catfish diet, or commercial dry dog food. Fresh animal products such as minced fish or beef liver can be added but can cause toxic growth. Live foods are also available. Nursery prawns are fed 10 to 20 per cent total body weight per tank once to twice per day, adjusted for growth and amount fed versus amount consumed.