Control of biofloc levels in shrimp farming and its implications for water quality and animal performance
Aquaculture has produced aquatic organisms by increasing the stocking density, reducing the occupation of areas and the use of water. The production of marine shrimp using biofloc technology (BFT) allows the practice of reducing water use, stimulating natural productivity that improves water quality and adds food to the target species. However, the maintenance of water throughout the cycle generates an increase in the amount of total suspended solids (TSS), which can interact with physical and chemical parameters, causing changes in water quality. A series of studies were carried out seeking to improve the management of suspended solids to improve water quality and optimize the production of marine shrimp, three at the Marine Aquaculture Station (IO-FURG, Brazil) and one at the Waddell Mariculture Center (WMC , USA).The thesis chapters, referring to experiments with Litopenaeus vannamei shrimp in BFT system, had as objective: (1) effect of two different flows of water pumping during the process of removal of suspended solids by sedimentation; (2) to analyze during the formation of bioflocs, the effect of different levels of suspended solids on the water quality and performance of the shrimp; (3) to evaluate the effect of different concentrations of suspended solids on oxygen consumption and zootechnical performance of shrimp; (4) evaluate the cultivation of marine shrimp, integrating tilapia for the biological treatment of SST, as well as the use of oysters as biofiltrators and the possibility of integrating a species of carnivorous fish to the BFT system. All experiments were carried out in greenhouses. In Chapter 1,a 17-week experiment was performed. A control without removal of solids was compared with two treatments with different pumping flows: high flow (HF) - 3945 L h-1 and low flow (LF) - 1750 L h-1 for removal of solids. Better zootechnical performance indexes of L. vannamei were achieved with the removal of solids. The treatment with less water flow in the clarifier facilitated sedimentation. In Chapter 2, three OSH ranges were compared over 42 days outlined in three treatments: low range (TL) 100 - 300 mgL-1, medium range (TM) 300 - 600mgL-1 (TM) and high range (TH) 600 - 1000mgL-1. The water quality parameters in the smallest range (TL) resulted in better L performance. vannamei. In Chapter 3, the shrimp were kept at five levels of SST: 250, 500, 1000, 2000 and 4000 mgL-1.A test was performed to measure the specific oxygen consumption (CEO) of the shrimp 24 and 42 days after the beginning of the experiment. The performance was similar in the five SST concentrations. Analyzes of CEO and performance data suggest an adaptation of L. vannamei in low concentrations of dissolved oxygen. In Chapter 4, two integrated multitrophic systems were assembled with water recirculating in four closed circuits composed of separate tanks for shrimp, tilapia, sedimentation tanks and red drumassociated with oysters. The study showed that the application of marine shrimp farming with biofloc technology in an integrated multitrophic system results in the reduction of solids caused by organisms that consume shrimp by-products. As conclusion,research has shown that OSH control can be accomplished by clarification, which can increase the efficiency of the sedimentation process by adjusting the flow maintained in the clarifier or by biological treatment using organisms that consume residues from shrimp production. The management of SST concentrations during the cultivation of L. vannamei in a BFT system generates benefits in water quality and improves zootechnical performance indexes.