Prawns, or as they are more commonly known in the United States as shrimp are decapod crustaceans that can live in either freshwater or salt water. There are over 540 sub species of prawn, ranging from almost invisible to the naked eye through a scant few millimeters to over a foot in size. Prawns and shrimp are not actually identical despite the linguistic mix up however aquaculture uses the term prawn specifically for freshwater forms of palaemonids and shrimp exclusively for marine penaeids. Prawns are an easy addition to an established aquaponics systems and are fairly simple starter creatures depending on species but they can be a hassle to grow successfully in larger quantities.
Prawns work great in an aquaponics system because they are detrivores, meaning they eat organic waste such as dead roots, flies, or anything else that has sunk to the bottom of the tank to decay. With this in mind is it unnecessary to specifically feed prawns as they will help keep the tanks free of wastage from the plants above.
Aquaponic prawns are a great species because they do not require additional nutrients or food and are an added bonus in the long run…By breaking up the rotting detritus they not only keep the tank cleaner they also recycle the plants own waste and give in back in the nutrients they excrete. The prawns themselves do not damage the plant roots although they will find them a great place to hide. Freshwater prawns can be somewhat trickier to breed because of the brackish water phase in their life cycle requiring an external hatchery. With that in mind it may not be so cost effective when it comes to freshwater prawn since you may have to constantly buy new stock and prawns alone will not usually produce enough waste to support most plants.
It is important to take several things into account when deciding on using prawns in an aquaponics system. Some forms of fish, Tilapia for example, love to eat prawns for dinner, and you will simply be wasting your money adding them in to the environment unless you use them as food. It is important to keep the prawns separate from other species because of this. In addition keeping prawns separate from themselves can be a challenge for most. Prawns are notoriously territorial creatures and will happily cannibalize each other if there is over crowding.
Normally breeders raise juvenile prawns at 3 to 4 per square yard of pond space and then harvest at 1 or 2 per yard. Harvesting only half of the stock keeps the prawn numbers in check to prevents over crowding and competition for available space…For a prawn aquaculture to be successful often commercial breeders have to have acres of space dedicated to prawns alone to provide sufficient numbers with each harvest.
Some have suggested that it is possible to grow prawns alongside fish like Tilapia by placing a two layer netting system that allows the the Tilapia to swim above the prawns but the harvesting can be dubious and difficult. Other suggestions have including using a “prawn cage” that can be raised up for harvesting. In a perfect equation 1000 shrimp would grow to a harvestable size in 4 months producing 100 pounds of shrimp if you have 10 shrimp to the pound but that is not usually the case. To successfully grow that number of shrimp you would need approximately 170 square yards of water with a density of three per yard to successfully raise the prawns and harvest only 50%. It is easy to see where most people do not decide to use aquaponic prawns in their system since there is such a low return on investment.
Prawns can be a fiddly addition to an aquaponics system, and can be especially cost ineffective if they are raised only in small numbers. The fact that they are detrivores and that they are able to be harvested quickly does make them a great addition to an aquaponics system but don’t expect to be eating prawns every night.