Quality of lettuce (Lactuca sativa L.) grown in aquaponic and hydroponic systems

Aquaponics is the integration of aquaculture and hydroponic systems where, in general terms, the waste produced by aquatic organisms becomes nutrients through bacterial action for plant growth. Water consumption as well as the environmental impact in this type of system are lower compared to more traditional hydroponic and aquaculture counterparts, due to its dual productive nature and closed condition of the system allowing the reuse of water and fish waste. The present study evaluated the yield, nitrate concentration, microbiological and functional quality of lettuce (Lactuca sativa L.) grown in two production systems: aquaponics and hydroponics. At the same time, fresh mass gain and feed conversion ratio (FCR) of rainbow trout (Oncorhynchus mykiss) were assessed. Lettuces were grown in an aquaponic system using waste water from the fish system, as well as in a hydroponic system with nutrient solution (Hoagland II-modified) both for 21 days. At the end of this period, baby lettuce (8 and 12 cm of length) was harvested. The yield of lettuce grown in aquaponic system was 6.73% higher than that of grown in hydroponic system. Also aquaponically grown lettuce had lower nitrate concentration (1079 mg kg-1 FW) than hydroponically grown lettuce (1229 mg kg-1 FW). Lettuces grown in both systems showed no significant differences in the microbial and functional qualities. Rainbow trout in the aquaponic system increased 13.6 g over 27.1±0.8 g initial fresh weight, obtaining a FCR of 0.74 after the experiment. These results indicate that the aquaponic system used in the present study is a sustainable alternative for the production of high quality lettuce considering its high yield, lower concentration of nitrates and similar microbiological and functional qualities compared to hydroponic systems, while allowing simultaneous fish farming with a good feed conversion ratio (74 g of food was needed to produce 100 g of rainbow trout).