The aim of this study was to evaluate the effect of predominantly chemoautotrophic and heterotrophic biofloc systems on ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and planktonic microorganisms in an integrated Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. Shrimp and tilapia were stocked at a density of 400 shrimp m⁻² and 45 fish m⁻³, respectively. The trial consisted of two biofloc treatments, with three replicates each: chemoautotrophic and heterotrophic. The identification and quantification of the planktonic microorganisms (ciliates, flagellates, microalgae, and total bacteria) and nitrifying bacteria were carried out through direct counting and fluorescence in situ hybridization, respectively. At the end of the trial, heterotrophic treatment had resulted in higher total abundance of bacteria. The relative abundance of AOB and NOB in relation to the total abundance was less than 0.1% for both treatments. The system was dominated by flagellates in both treatment groups. The abundance of microalgae and ciliates was higher with chemoautotrophic treatment. After 43 days, the shrimp weights were higher in the chemoautotrophic group, while the final weights of the tilapia were not significantly different between the two treatments. The type of biofloc system (Chemoautotrophic vs. Heterotrophic) did not significantly alter the establishment of AOB and NOB in a Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. The two treatments proved to be equally efficient for maintaining good water quality, but the chemoautotrophic treatment resulted in better shrimp growth. Thus, our study demonstrated that chemoautotrophic biofloc is a promising approach in integrated multitrophic aquaculture.

One of the most critical factors in aquaculture production is the concentration of dissolved oxygen (DO). Biofloc technology (BFT) systems rely on blowers and pumps to introduce oxygen into the medium. Problems in aeration systems can lead to a decrease in DO levels, leading the system to a state of hypoxia that results in mortality in production. The objective of this work was to determine the effect of different reoxygenation methods on the survival of P. vannamei shrimp in BFT systems. Twelve experimental units of 20 L were used, maintained at 28 °C, with a stocking density of 600 shrimp/m3 and total suspended solids (TSS) of 500 mg/L. Oxygen supply was interrupted until a concentration of 1.5 mg/L was reached (controlled hypoxia), followed by the application of four reoxygenation strategies: abrupt reoxygenation (AR), gradual reoxygenation (GR), liquid hydrogen peroxide (LHP), and powdered hydrogen peroxide (PHP). Survival was observed for 72 hours after reoxygenation and was affected by the critical drop in dissolved oxygen (DO) and subsequent reoxygenation, although no statistically significant differences were observed between treatments (p > 0.05). The RA and RPH treatments showed the lowest mean survival rates (59.26% ± 12.83% and 61.12% ± 7.86%, respectively), followed by RPP (70.37% ± 6.41%) and gradual reoxygenation (GR), which had the highest survival rate (74.08% ± 7.86%). Despite statistical equivalence, a clear trend of physiological superiority was observed in the GR and RPP methods, which stood out for their better metabolic stability and lower oxidative impact. The hepatopancreas was 3.23 times more susceptible to lipid peroxidation than muscle tissue, confirming its greater sensitivity to oxidative stress. The levels of thiobarbituric acid reactive substances (TBARS) showed a significant reduction after 72 hours in the RG and RPP treatments, suggesting partial resolution of oxidative damage and activation of antioxidant mechanisms. This adaptive response indicates redox reorganization and restoration of homeostasis. The results demonstrate that the kinetics and modality of reoxygenation are crucial for measuring the intensity of oxidative stress and for defining the recovery capacity of shrimp.