EVALUATION OF FOOD SAFETY RISKS IN AQUAPONIC PRODUCTION OF VEGETABLES AND TILAPIA

Aquaponics is the integration of aquaculture and hydroponics that is now being used as a model for sustainable food production. Because fresh vegetables are usually consumed raw, there are concerns about food safety and zoonotic risks from fish waste in aquaponic production. The purpose of this study was to determine the survival, persistence, and transfer via root uptake of an attenuated Salmonella strain in a recirculating aquaponic system (RAS) used for leafy green production in order to gain the knowledge of good agricultural practices specific for aquaponic practitioners to reduce the potential for foodborne illnesses due to product contamination.

A prototype RAS for experimental trials was designed and built at the Center for Aquatic Biology and Aquaculture (CABA) facility at UC Davis (Figure). Initially, the lethal and infective dose of Salmonella enterica serovar Typhimurium (aPTVS177) strain to naïve tilapia (Oreochromis spp.) fingerlings was determined by intra-gastric challenge. Using two (high and low) non-lethal doses, a second group of fish was challenged and used in a laboratory controlled RAS growing hydroponic lettuce. Salmonella was quantified in the system components (tanks, tubing, plant bed substrate), fish waste (feces), and lettuce plants (roots and leaves) using microbiological and molecular analysis. We determined that the three highest inoculum doses (10⁸-10¹⁰ CFU) resulted in fish with Salmonella positive gastrointestinal tracts and associated tissues. Salmonella recovery during phase 2 is shown in Table 1. On day 42 (harvest), lettuce leaves, roots, pots, and rafts were negative; two fish had positive stomach and intestinal tissues. Data from this study will fill knowledge gaps regarding how foodborne pathogens may persist and move through an aquaponic system.