Abstract
In this study, the ecotechnology artificial floating islands (AFIs), colonized by Eichhornia crassipes, have been tested as a tool for water quality improvement of fishponds. The experiment was carried out in semi-intensive production during the grow-out period of Nile tilapia, comprising one production cycle. It was completely randomized with two treatments (with and without AFIs) and three replications. Temperature, dissolved oxygen, conductivity, pH, turbidity, total dissolved solids (TDS), transparency (Secchi) and concentrations of chlorophyll a (CL a), total nitrogen (TN), total ammonia nitrogen (TAN), total phosphorus (TP) and orthophosphate (PO43--P) were analyzed fortnightly in the fishponds. Two groups ordered based on environmental characteristics were formed by applying the Principal Component Analysis (70.68% of explicability). The fishponds with AFIs were assigned to higher values of Secchi and lower values of pH, turbidity, TDS and concentrations of nutrients. On the other hand, the fishponds without AFIs were assigned to the highest values of these variables, except for Secchi. In 30 days, the AFIs showed the lowest concentrations of TP and PO43--P, and for CL a, TN and TAN, the differences were recorded after 90 days. The use of AFIs has demonstrated potential to conserve water quality in fishponds, notably for biologically assimilable elements (PO43--P and TAN) and for those directly related to eutrophication (P and N). Artificial floating islands should be encouraged for small and medium-sized farmers as tool to improve water quality in fishponds. However, new AFIs coverage rates must be evaluated, as well as the control of hydraulic retention rates.
 Keywords: aquaculture, ecotechnology, free-floating aquatic macrophytes.
Highlights
Brazilian aquaculture has developed rapidly, attaining, in 2016, 13th place among the largest producers in the world (FAO, 2018)
The results of limnological variables observed in the Nile tilapia fishponds with or without artificial floating islands (AFIs) are within the ideal range for tropical fish production when compared to specialized literature (Table 2)
The artificial floating island technology used in this study improved the water quality of the Nile tilapia fishponds, significantly reducing concentrations of total nitrogen (TN), total ammonia nitrogen (TAN), NH+4-N, NH3-N, total phosphorus (TP), PO43--P and chlorophyll a, without affecting zootechnical performance of fish that achieved a yield considered satisfactory for the species (Pezzato et al, 2004; Luz and Portella, 2005)
Summary
Brazilian aquaculture has developed rapidly, attaining, in 2016, 13th place among the largest producers in the world (FAO, 2018). In 2019, fish production increased 4.9% in relation to the previous year, reaching a yield of 758,006 tons, even in a scenario of low national economic growth. This increase represents the importance of the sector for the country, which is the 4th largest producer of tilapia in the world (PeixeBr, 2020). Overfeeding or the use of unbalanced feed reduces the absorption of nutrients by fish, which can result in excess of organic matter and nutrients in production systems, with direct consequences on water quality, favoring their assimilation by phytoplankton and aquatic
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