Use of different periodic strategies of initial organic fertilization in nurseries covered in the fattening phase of white shrimp Litopenaeus vannamei (Boone, 1931) in a biofloc system
Organic fertilization induces the establishment of microorganisms that contribute to water quality, feed source and increased survival of the target organism. The objective of the present work was to evaluate the efficiency in the development of the microbial community and the effect on the zootechnical performance in the fattening phase of the marine shrimp Litopenaeus vannamei in a biofloc system with two different strategies of initial organic fertilization. The experimental design consisted of two treatments with four replicates. Treatment B3: Initial fertilization was done for three days prior to settling. Treatment B30: initial fertilization performed for 30 days prior to storage. Juveniles (1.73 g ± 0.9) were stored in eight 600 m2 nurseries at density of 75 m-2 shrimp. The shrimp were fed twice a day with commercial feed containing 38% crude protein (Guabi®), following feeding table and daily observations of food consumption, and physical and chemical parameters of the water were monitored during the thirteen weeks of experiment (91 days). Water samples were collected for microbial community analysis. A significant difference was observed for the performance of the treatments B3 and B30 (P <0.05) for survival (69.13% ± 7.96 and 78.76% ± 1.34, respectively) and productivity (5. 80 ton / ha ± 0.78 and 6.84 ton / ha ± 0.14, respectively). While the B30 treatment obtained higher final weight (11.58 g ± 0.44) and lower apparent feed conversion (1.51 ± 0.01). Both treatments had a higher amount of chlorophytes than the cyanobacteria and during the B30 treatment period there was a greater abundance of microorganisms such as rotifers, ciliates, flagellates, amoebae and until the middle of the experimental period the presence of nematodes. From the results obtained it was possible to conclude that the use of initial fertilization during the 30 days before settlement is a better option for the development of the microbial community and effective to avoid high concentrations of cyanobacteria, providing better quality of water throughout the culture.