Economic viability of the integrated production of shrimp Macrobrachium rosenbergii and lettuce Lactuca sativa L. in an aquaponics system
Aquaculture water is generally rich in nutrients, especially nitrogen and phosphorus compounds, with great potential for use in the production of hydroponic vegetables. At the IO Marine Aquaculture Station - FURG, Rio Grande, RS, a study was carried out to assess the feasibility of integrated production of Lactuca sativa lettuce and Macrobrachium rosenbergii shrimp. The effects on the water quality of different lettuce densities in a nursery production system, zootechnical performance of postlarvae of M. rosenbergii, performance of lettuce plants of the smooth variety L. sativa L. and its economic viability were verified. Postlarvae of M. rosenbergii (0.073g ± 0.04g) with a stocking density of 2 shrimp / L were used in twelve 50 liter tanks interconnected to 12 liter tanks with lettuce seedlings to act as biological filters, constituting a recirculation system (RAS). The entire system was covered by a rectangular greenhouse, with four treatments with three replications, divided into: RAS treatment or control, without any lettuce included in the recirculation system; Treatment 50, with 50 lettuces introduced into the filter; Treatment 25, with 25 lettuces introduced into the filter; Treatment 13, with 13 lettuces introduced into the filter. Water temperature, dissolved oxygen and pH were monitored daily. While NAT, NO2-, NO3- and PO4- were monitored three times a week and alkalinity and hardness, twice a week. The results were analyzed by a one-way analysis of variance (ANOVA) and Tukey test (α=0.05). With the results obtained for productivity, survival and weight gain, for both shrimp and plants, three different economic analyzes were performed: cost-return analysis, cash flow analysis for the ten-year horizon and analysis of economic feasibility of the project, all analyzes made under the four treatments as if they were the scenarios for a small producer. Shrimp survival and final weight were adequate as expected for the time of the experiment, while lettuces had a lower performance, demonstrating a need for mineral supplementation for their production. For the economic analysis, the scenario based on the experiment's treatment 50 stands out both among the economic and feasibility indicators, and in the 10-year horizon. Even though the disbursement for this scenario is the second largest among them, its profit is greater, making it more efficient to dilute these expenses.