Oysters have the potential to be a part of more sustainable farming systems, such as multitrophic systems integrated into biofloc systems, due to their filtration activity, which enables them to act as organic consumers. However, the stress experienced by animals in a system with a high organic load can compromise their productive performance. The objective of this study was to evaluate the biological responses of Crassostrea gasar oysters when exposed to different concentrations of total suspended solids in biofloc systems. The oysters were exposed to four different concentrations of solids for 28 days. Hall effect sensors were installed on the outside of the shells to detect the movement of the oyster valves. Also, biochemical and histological analyses were conducted to assess the biological responses of the oysters to exposure to varying levels of solids. A difference in valve opening detected by the Hall sensors was observed from the second week of culture, indicating a relationship between shell closure and higher concentrations of suspended solids present in the system. In terms of biochemical analysis, a significant increase in lipid damage was observed in treatments with medium and high levels of total suspended solids compared with the control group. Conversely, no changes were observed in the gill structure of the oysters caused by the concentrations of suspended solids in the system when compared with the control. According to the analyses of gill activity and biochemistry, it is suggested that C. gasar should be cultured with total suspended solids at less than 200 mg/L. Oysters cultivated in a biofloc system keep their shells closed when subjected to high concentrations of total suspended solids; concentrations of total suspended solids below 200 mg/L do not induce oxidative stress, changes in behavior or histological alterations in C. gasar oysters cultivated in a biofloc system.

The biofloc technology (BFT) system is widely used in aquaculture for the cultivation of Pacific white shrimp (Penaeus vannamei). While the practice of reusing percentages of water from previous crops to initiate the system is common, this study aimed to determine the minimum inoculum of total suspended solids (TSS) required for the rapid stabilization of nitrogen compounds and the bacterial community. The experiment was conducted in 400 L experimental units stocked with juvenile P. vannamei. We compared six treatments with different initial inoculum concentrations: control (0 mg/L), 2.5 mg/L, 5 mg/L, 10 mg/L, 20 mg/L, and 40 mg/L. These concentrations corresponded to inoculations of 0%, 0.625%, 1.25%, 2.5%, 5%, and 10% of mature biofloc water with an initial TSS concentration of 400 mg/L. Treatments with an inoculum showed a more effective oxidation of ammonia and nitrite compared to the control. However, the 2.5 mg/L treatment differed significantly (p < 0.05) from the other inoculated treatments, exhibiting persistently high ammonia concentrations and a slower stabilization time. Survival rates in the 5, 10, 20, and 40 mg/L treatments were significantly higher (p < 0.05) than in the control and 2.5 mg/L treatments, remaining around 95%, while the latter had survival rates of 48.75% and 65.83%, respectively. The final biomass were as follows: control: 479.7 ± 30 g; 2.5 mg 628.1 ± 93.3 g; 5 mg 976.5 ± 128.1 g; 10 mg 850.3 ± 158.1 g; 20 mg 789.6 ± 122.7 g; 40 mg 856 ± 96.9 g. Final biomass and productivity were highest in the 5 mg/L treatment and did not differ significantly among the 10, 20, and 40 mg/L treatments. The results suggest that in a BFT system for P. vannamei, a minimum inoculum of 5 mg/L of TSS is sufficient to achieve high water quality and superior zootechnical performance.