Effect of microbial aggregate size on the nitrification process during the production of white shrimp Litopenaeus vannamei in a biofloc system (Biofloc Technology - BFT)
The main feature of the biofloc shrimp production system (Biofloc Technology System - BTF) is the minimum water change. The accumulation of nitrogenous compounds can cause damage, since ammonia and nitrite, when present in high concentrations, cause toxic effects for the produced organisms. Nitrifying microorganisms are efficient in removing ammonia and nitrite, however they are extremely sensitive to various factors such as pH, oxygen, temperature, among others, and in BFT systems there are indications that the size of the Biofloc particles can affect the nitrification activity. Thus, this dissertation aimed to evaluate, in three experiments, if the size of the bioflocs affects the nitrification process in the cultivation of Litopenaeus vannamei. In experiment 1,the bioflocs were separated through constant filtration with different mesh sizes, this being composed of four treatments: 50, 150 and 300 μm meshes, and the control treatment without filtration - SF In experiment 2, carried out with larger meshes, the bioflocs were separated in treatments with 300 and 600 μm meshes, and the control treatment - SF Experiment 3 aimed to evaluate the recovery of Bioflocs when they are reduced in size, together with the nitrification process, this experiment was composed of three treatments, the treatment where there was partial filtration of 50 μm mesh bioflocs for five days, the treatment with constant filtration with 150 μm mesh, and the control treatment - SF The results of these three experiments indicate that the size of the bioflocs,as well as the amount of material in suspension, do not affect the nitrification process in the BFT system. In all experiments, the water quality parameters were within the ideal ranges for the production of L. vannamei. Regarding zootechnical performance, the best results were obtained in treatments where there was no filtration - SF in the three experiments. This was due to the greater availability of bioflocs in these treatments, directly reflecting better rates of weight gain and feed conversion.