7.4.6 Prawns

Main commercial type:
Giant river prawn (Macrobrachium rosenbergii)

FIGURE 7.12
Line drawing and photograph of a giant river prawn (Macrobrachium rosenbergii)

Description

The term prawn refers to a very diverse group of stalk-eyed freshwater decapod crustaceans with long narrow muscular abdomens, long antenna and slender legs (Figure 7.12). They can be found feeding on the bottom of most coastlines and estuaries, as well as in freshwater systems. They usually live from one to seven years, and most species are omnivores. Shrimp and prawns, respectively, commonly refer to saltwater and freshwater species, although these names are often confused, especially in the culinary sense.

Prawns can be a great addition to an aquaponic system. They consume uneaten fish food, fish waste and whatever organic material they find in the water or on the bottom. As such, they help to clean and support system health, and accelerate organic material decomposition. It is better to grow prawns and mid-water fish simultaneously in an aquaponic system, as prawns cannot be grown in high enough densities to produce adequate wastes for the plants. Prawns are very territorial, so they need a substantial allocation of lateral space; the horizontal surface area determines the number of individuals that can be raised, although stacked layers of netting can increase surface area and increase quantity. Some polyculture systems with tilapia have been tested with various degree of success, although the number of individual that can be stocked is low. Most prawns have similar needs, which include hard water, warm temperatures (24-31 C) and good water quality, but the conditions should be adjusted for the particular species grown.
In ideal conditions, prawns have a four-month growing cycle, meaning it is theoretically possible to grow three crops annually. Prawn post-larvae need to be purchased from a hatchery. The larval cycle of prawns is fairly complex, requiring carefully monitored water quality and special feed. Although possible on a small-scale, breeding prawns is only recommended for experts. Because they can eat the roots of the plants, prawns should be grown in the fish tanks only.