EVALUATION OF THE POTENTIAL PREDATOR-PREY RELATIONSHIP OF Procambarus clarkii AND Litopenaeus vannamei IN A LOW SALINITY RECIRCULATING TANK SYSTEM

Polyculture of Pacific white shrimp (Litopenaeus vannamei) and red swamp crayfish (Procambarus clarkii) is a new production strategy being explored by commercial shrimp farmers in west Alabama. Crayfish are being produced on a pilot-scale in earthen ponds and a split-pond on one commercial shrimp farm. Since crayfish can freely cross levee systems into other ponds, hence it is important to understand the predator-prey relationship between these two species. Traditional crawfish production relies on pond primary productivity to fuel growth and reproduction of the crop, while low salinity shrimp culture involves annual stocking of post-larvae and supplemental feeding with a commercial diet. In these production systems, the growth of the crawfish population could be fueled by the primary productivity that results as a byproduct of the semi-intensive nature of shrimp culture. The main area of concern is that crawfish are known to feed on small fish and insects in addition to detritus and plant material. This feeding strategy raises the question of whether crawfish would feed on juvenile shrimp, causing a negative impact on shrimp production. In order to investigate the potential for these two species to develop a predator-prey relationship, a controlled experiment was set up using a recirculating system. The system consisted of 24 aquaria (75 L) that were continuously recirculated through a sand filter and biofilter. The salinity was maintained at approximately 2.3 g/L using reconstituted seawater. Three distinct treatments were used to evaluate the impact of crawfish presence on shrimp survival including a Treatment A - Control (20 shrimp + daily feed ration), Treatment B (20 shrimp and one crawfish both receiving a daily feed ration), and Treatment C (20 shrimp and one crawfish with only the shrimp receiving a daily feed ration). Eight replicates of each treatment were randomly assigned tanks and stocked on August 6, 2019. Shrimp and crawfish were fed a calculated ration twice daily. Following 21 days of culture the tanks were harvested and the total number of shrimp and crawfish were enumerated and group weighed to determine growth, feed conversion ratio, and survival. Shrimp survival in the control group was significantly higher (91.9%) than the other treatments (P<0.001)(Treatment B = 58.8%, and Treatment C = 40.6%). These results indicate a significant reduction in shrimp survival in the presence of crawfish. This negative effect was further increased in the treatments where feed rations intended for the crawfish were absent.