3.4. Training and maintenance of microbial aggregates (biofloc) generated in the super intensive cultivation system of post-larvae of marine shrimp
The dissolved oxygen of the aquariums in the test for formation and maintenance of microbial aggregates was between 5.80 and 5.84 mg.L− 1 and the temperature was between 26.7 and 29.6 °C in all treatments and the control. A significant difference (p = 0.017) was observed only in the microbiological count of the water on the seventh day of testing, when the total count of Vibrio spp. in the water was lower in the groups treated with Bacillus spp. (1 × 104 CFU·mL− 1) and the commercial product Comambio (1 × 104 CFU·mL− 1) than in the control (Fig. 1), there was no statistical difference in the total count of viable heterotrophic bacteria. These results corroborate with the data of V. alginolyticus inhibition in vitro by Bacillus spp. isolates. Several studies were performed with Bacillus spp., as it is known that its indirect effect on improving water and soil quality inhibits pathogens in fish and shrimp cultures. Bacillus subtilis, B. cereus and B. licheniformis showed a synergistic reduction in pathogen load and the concentrations of ion residues in vitro and in vivo in the culture of Cyprinus carpio ornamental fish ( Lalloo et al., 2007). Weekly applications of commercial bioremediator (BZT Aquaculture) with Bacillus and Nitrobacter strains, reduced the number of Vibrio species compared to the control (without product) and also increased the survival and production of Penaeus monodon ( Janeo et al., 2009). Nimrat et al. (2008) found that treatment with soil drying and addition of the commercial product (A Probiotic), and Bacillus spp. being the main microorganism, decreased the count of Vibrio and Pseudomonas species in P. monodon farm soil. The use of Bacillus pumilus consortia and periphyton microalgae in the culture of P. monodon decreased the count of Vibrio compared to the control ( Banerjee et al., 2010). Therefore, the application of microorganisms to reduce the number of pathogenic bacteria offers a great advantage to marine shrimp farming.