POLYCULTURE OF RED SWAMP CRAWFISH Procambarus clarkii AND PACIFIC WHITE SHRIMP Litopenaeus vannamei CULTURED IN LOW SALINITY WATER

Polyculture of Pacific white shrimp (Litopenaeus vannamei) and red swamp crawfish (Procambarus clarkii) is a new production strategy being explored by commercial shrimp farmers in west Alabama. Crawfish are being produced on a pilot-scale in earthen ponds and a split pond on one commercial shrimp farm. Traditional crawfish production relies on pond primary productivity to fuel the crop growth and reproduction, while low salinity shrimp culture involves annual stocking and supplemental feeding. The excess nutrients generated during shrimp production may be beneficial to crawfish growth. The main area of concern is that crawfish are known to feed on small fish, insects, detritus and plant material. This feeding strategy raises the question of whether crawfish would feed on juvenile shrimp, causing a negative impact on shrimp survival and production. Two controlled experiments were set up using two different systems to investigate the polyculture potential for these two species. The first experiment consisted of a 24-tank system (75 L per aquaria; 3900 L total system volume) with water recirculated through a sand filter, biofilter, and sump. The salinity was maintained at approximately 2.3 g/L using reconstituted seawater. The second experiment used a green water on-levee flow-through tank system (twelve 800-L tanks) at Greene Prairie Aquafarm in west Alabama. The shrimp production pond that supplied water to this system had a salinity of 2 g/L. In this green water system, pond water was pumped into the tanks (4.9 L/min) and drained back into a shrimp production pond. In both trials, three treatments were used to evaluate the impact of crawfish presence on shrimp survival. Eight replicates of each treatment were stocked (0.53 g mean initial weight) in the aquarium system. Following 21 days of culture, shrimp were harvested and evaluated for survival and growth. The green water system was stocked (0.15 g mean initial weight) using four replicates of similar treatments. The first experiment indicated crawfish presence had a significant negative effect on shrimp survival (Treatment A= 91.9%, Treatment B = 58.8%, Treatment C = 40.6%) (P<0.001). However, the second experiment showed no significant differences among treatments for survival or growth. These results indicate that although crawfish will prey on shrimp in a clear water system, the need or ability to prey on shrimp did not occur in a green water system.