Effect of hydrogen peroxide on the microbial community present in shrimp production systems Litopenaeus vannamei with bioflocs
The technique of producing aquatic organisms without water renewal, with high stocking densities, strong aeration and predominantly aerobic and heterotrophic biota, forming microbial aggregates or flakes, was known as ZEAH (“Zero Exchange Aerobic Heterotrophic culture systems”) and, more recently, known as biofloc technology (“Biofloc Technology” - BFT). Due to the presence of a rich microbial community (microalgae, protozoa and some metazoans), bioflocals have high nutritional levels. This community can also lead to accelerated consumption of oxygen, quickly leading to the death of the produced organism. In cases of emergency caused by a lack of electricity, or a defect in the aeration system,the researchers guarantee the survival of the shrimp during the inoperability of the system through the application of hydrogen peroxide (H2O2). However, H2O2, as a neutral charge molecule, has an easy way to cross the cell membrane by diffusion and, inside cells, produces the peroxidation of lipids and proteins, affecting cell integrity. The objective of this work was to evaluate the effect of the application of hydrogen peroxide on microorganisms present in the creation of L. vannamei in BFT medium, to characterize the protozoa community by optical microscopy before and after the application of hydrogen peroxide and to estimate the recovery time of this community after using peroxide for increasing periods. For this purpose, four treatments were tested in 12 45 L boxes with a density of 300 shrimp per cubic meter,that comprised the Control, with normal aeration (without H2O2 application) and the 12-hour, 24-hour and 48-hour treatments, where peroxide (10μL H2O2 L-1) was applied during these periods whenever necessary to maintain the dissolved oxygen levels above 6 mg L-1. The means of dissolved oxygen did not differ significantly, but following applications we can identify some specific variations. The means of the water quality parameters were significantly different between the Control and the other treatments. Total suspended solids (TSS) were significantly higher in the 12-hour treatment than in the others. It was found that the addition of H2O2 affected the nitrification process in the BFT system and indirectly affected the shrimp,resulting in less growth performance and weight gain in treatments where hydrogen peroxide was added. It was also found that there was a rapid recovery of ammonium-oxidizing bacteria, but not nitrite-oxidizing. The phytoplankton present in the culture medium resisted the application of H2O2 well, with some effect only on Chlorophycea Planctonema sp., Where the control showed greater abundances than in the 24-hour and 48-hour treatments. After that, a decrease in its abundance probably occurred due to the low luminosity caused by the high concentration of SST. It is concluded that the addition of hydrogen peroxide causes temporary damage to microorganisms, especially nitrifying bacteria, but this is partially reversed in a few days after the application of this element ceases.There was also no cumulative effect with the application of peroxide for a longer time.