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

Abstract

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).

Effects of stocking density on the growth and flesh quality of rainbow trout (Oncorhynchus mykiss) reared in a low-tech aquaponic system

“…Under the conditions of the present study, the average mesophilic count (reported as TVC) at harvest in the lettuce rinsate (5.65 Log 10 CFU mL − 1 ) was comparable to the values measured after 63 days (4.5 Log 10 CFU g − 1 ) but higher than those after 118 days of cultivation (2.8-3.5 Log 10 CFU g − 1 ) in a previous study cultivating lettuce in aquaponics (Elumalai et al, 2017). Moreover, we did not find differences in the counts of mesophilic bacteria and Enterobacteriaceae between lettuce leaves produced in aquaponics or in hydroponics as already found by Alcarraz et al (2019) who did not find differences neither in psychrophilic bacteria. Finally, in lettuce, as with fish samples, the absence of faecal indicator bacteria, such as E. coli, suggests the aquaponic system was suitably hygienic (Elumalai et al, 2017).…”

“…The mortality rate was very low (3.3% on average), as previously observed for Cyprinus carpio farmed in the same aquaponic system at similar stocking densities (initial values: 2.5 and 4.6 kg m − 3 ; final values: 6.9 and 11.5 kg m − 3 ) (Maucieri et al, 2019). To our knowledge, only one study is available concerning trout reared in aquaponic systems focused on microbiological analysis of lettuce (Alcarraz et al, 2019), whereas commercial aquaponics systems are successfully working in Columbia, Chile and Canada. Other authors found that the mortality rate simultaneously increased when the initial stocking density increased, both in Cyprinus carpio var.…”

Microbial Origin of Aquaponic Water Suppressiveness against Pythium aphanidermatum Lettuce Root Rot Disease

“…This could be logical because AP water contained lower concentration of mineral nutrients. However, this is in contradiction with other papers where yields of AP were similar to HP, and CAP yields better than AP [65][66][67][68][69][70]. In these papers, authors explained this contradiction (lower mineral nutrients concentrations but good yields) by the potential presence of microorganisms or compounds able to increase plant growth [71].…”

Characterizing Nutrient Composition and Concentration in Tomato-, Basil-, and Lettuce-Based Aquaponic and Hydroponic Systems

“…Similarly, yields of leafy vegetables (i.e., basil and kale) and fruity vegetables (i.e., tomato and pepper) were lower in a simulated aquaponic solution (low EC and high pH) than in hydroponics (well water was used) [12]. On the contrary, the growth and yield of lettuce grown in aquaponics were higher than those grown in hydroponics (tap water was used) [13]. Savidov et al (2007) [14] claimed that the yield of aquaponic tomato and mini-cucumber exceeded the reported yield of commercial hydroponic crops; however, actual yield comparisons were not made between the systems.…”