OBSERVATIONS ON THE BEHAVIOR AND FOOD PREFERENCES OF Macrobrachium rosenbergii IN DEEP WATER CULTURE AQUAPONIC GROW BEDS IN ARIZONA

Thanks to the donation of 130 juveniles to the aquaponics class at the Mesa Community College Center for Urban Agriculture, in the fall of 2017, the opportunity arose to observe the behavior of the freshwater prawn Macrobrachium rosenbergii in two Deep Water aquaponic culture beds. Slightly different in size and method, the first was a classic miniaturized version of the University of Virgin Island technique with an 18 inches deep grow bed tank (0.42 m) with 40 ft2 (3.71 m²) of grow bed space. The second system with a depth of 21 inches (0.53 m) and 32 ft² of grow bed space (2.97 m²) was a new technique called Self Contained Aquaponics (S-CAp) designed to easily convert existing small splash pools to aquaponic mini-farms.

Each system was stocked at a rate of 1.5 juvenile prawns per ft² of grow bed surface area (16.15/ m2) resulting in 60 prawns in the UVI style-DWC and 48 prawns in the S-CAp).  Stocked on August 7^th 2017 they were maintained in the DWC beds until harvest when the tank water began to dip below 70 F/21 C on November 1^st and 3^rd 2017.  Each grow bed was planted with two types of tomatoes, collard greens, broccoli, zinnias, pima lima beans, Armenian cucumbers, sweet potato vines. There were also guppies (Poecilia reticulata) stocked in the grow beds for mosquito control. Tilapia  (blue (Oreochromis aureus) x nile (O. niloticus) hybrid and goldfish  (Carassius auratus) were stocked in the system fish tanks (separate from the grow beds). The prawns were also provided 32% protein floating tilapia pellets to maximize the opportunity for good growth.

The observations were:

• Survival was 78% in the UVI and 197.7 grams and 58%/113.53 grams in the S-CAp with mean sizes of 4.12 grams and 4.05 grams respectively.
• The prawns showed a decided preference for plant roots over the floating pellets or even capturing the guppies for supplemental food to the point of inhibiting root development and overall plant growth.
• Of the plant roots, the prawns demonstrated a decided preference for the roots of the beans and tomatoes.
• By providing heads of red leaf lettuce for the prawns to eat eventually at a rate of 2 ½ pound heads per week, root growth in most species of plants was partially restored except for the beans and tomatoes.
• Once the prawns were harvested, plant grows accelerated significantly as demonstrated by the rapid development of new roots and leaves.