Evaluation of lettuce cultivation in an aquaponic system, with and without bioflocs, compared to a hydroponic system, in a greenhouse in southern Brazil

AbstractA recirculation system was set up to evaluate lettuce production (floating) in aquaponics (Aqua) and aquaponics with bioflocs (AquaFloc) in comparison to hydroponics (Hydro), in triplicate, for 45 days. Juvenile tambacu into the aquaponics tanks were fed with a commercial feed. Water quality was monitored and vegetable growth was evaluated. Head diameter, height, fresh matter, dry matter, number of leaves, and chlorophyll a+b concentration were higher (P<0.05) in “Hydro” than “AquaFloc”, even when the “AquaFloc” reached 60 days. The “AquaFloc” system presented 62% of fish survival, but presented lower (P<0.05) concentrations of ammonia and nitrite compared to “Hydro” and absence of nitrate. Electrical conductivity and concentration of total solids dissolved in water were lower (P<0.05) in “AquaFloc” than in “Hydro”, while pH was higher (P<0.05) in “AquaFloc” in comparison with “Hydro”, resulting in less availability of nutrients for plant growth. The “Aqua” system did not show lettuce growth and presented a complete fish mortality. The fish-vegetable ratio used did not meet the nutritional demand of the lettuces. New studies must be carried out with an appropriate fish-vegetable ratio that can provide sufficient nutrients to plants in aquaponics, with control of the system's pH.