Study of water quality and growth performance of common carp (Cyprinus carpio) in an aquaponic system with different densities of lettuce (Lactuca sativa)

Aquaponic system, which is a combination of recycling aquaculture and hydroponic plant cultivation, is consistent with the goals of sustainable development in the aquaculture industry. This experiment was conducted in the form of a completely randomized design with five experimental treatments and each treatment with three replications, which includes the control group: 30 carp (Cyprinus carpio) in a 300-liter tank (without lettuce), A1: 10 lettuce (Lactuca sativa) per m2 (without fish) along with liquid fertilizer, A2: 30 lettuce plants per m2 (without fish) along with liquid fertilizer, A3: 10 lettuce per m2 and 30 fish, and A4: 30 lettuce per m2 along with 30 fish for 60 days. The average weight of the fry fish (50.18 ± 1.23 g) and lettuce plant (10.32 ± 1.49 g) at the beginning of the experiment was the same in the experimental groups. The amount of dissolved oxygen in all experimental treatments was significantly higher than the control group (5.76±1.18 mg/liter) and the highest leve was obtained in A2 treatment (6.80±1.24 mg/liter) (p<0.05). At the end of the experiment, the average total suspended solids (1245.8±60.84 mg/liter), alkalinity (133.64±15.7 mg/liter), nitrite (0.18±0.04 mg/liter), and nitrate (62.40±2.15 mg/liter) were significantly higher in the control group (p<0.05) and the lowest values were seen in A2 treatment. There was no statistically significant difference regarding the performance of growth and feed utilization of the fish between the experimental treatments and the control group (p>0.05). However, the length and final weight of the plant and the relative growth rate of lettuce showed a significant difference between the experimental treatments and the control group (p<0.05) and the highest amount of the mentioned indicators was recorded in A4 treatment. To sum up, the results of this experiment showed that in the aquaponic system containing carp with a density of 100 carp per m2 and a density of 30 lettuce plants per m2, it leads to an improvement in the productivity of carp and lettuce production with proper water quality.