Improvement of management techniques in litopenaeus vannamei intensive nurseries in the biofloc system
The present study aims to evaluate a set of management practices for the improvement of the intensive production of the marine shrimp Litopenaeus vannamei kept in nurseries amid the bioflocs. For this study, experiments were carried out on a commercial scale at the Marine Aquaculture Station of the Institute of Oceanography at the Federal University of Rio Grande, RS, Brazil. The performance of each experiment is described in the following chapters: (1) Initial fertilization in intensive production nurseries of Litopenaeus vannamei in the biofloc system; (2) Removal and control of total suspended solids on a productive scale of Litopenaeus vannamei in the biofloc system in nurseries; (3) Management strategy to minimize problems with Nodularia spumigena cyanobacterial blooms in shrimp ponds in the BFT system.To carry out the experiments, 600 m2 rectangular excavated ponds were used, all of which were covered by geomembrane (HDPE) with an arrangement in a raceway system. Each nursery was equipped with 2 paddle wheel type aerators of 1.0 HP each. The animals were fed 38% crude protein and fertilized with molasses whenever necessary to control ammonia, with minimal or zero water changes. As the main results were observed in experiment 1, the use of biofloc inoculum associated with organic fertilization (molasses and feed) reduced the need to use water in renovations and molasses in fertilizations to control the increase in nitrogen concentrations and maintained the quality of adequate water during the fattening phase of L. vannamei. In experiment 2,the use of clarifiers promoted the management of concentrations of total suspended solids during the entire fattening phase, reduced the ratio of water use per kilo of shrimp produced and the effluent discharges, reinforcing the biosafety of the system, using a minimum volume of 0 , 46% clarification in relation to the volume of the production area. In experiment 3, organic fertilizations applied for three consecutive days at a C: N ratio of approximately 20: 1, after the occurrence of Nodularia spumigena cyanobacterial blooms, proved to be a viable alternative to contain blooms, favoring the development of chlorophyll microalgae and reducing the losses of zootechnical performance of the shrimp L. vannamei in a biofloc system.The results achieved in the present study contribute to the improvement of the management techniques applied in the large scale production of L. vannamei in intensive nurseries with bioflocs.