Effect of aeration intensity on the nitrification process of biofilm on the production of Litopenaeus vannamei (Boone, 1931) in a biofloc system and clear water
Artificial substrates have great importance for the establishment of the biofilm, and their use in the culture systems represents a complementary source of food, increase space for animals and aid in the metabolism of nitrogen compounds. Nitrifying bacteria present in biofilm play an important role in the maintenance of water quality, and several factors such as pH, temperature, salinity and dissolved oxygen can interfere in the establishment and efficiency of these bacterial communities. However, there is not much information in the literature on the influence of aeration intensity on the bacterial community present in the biofilm. Thus, the objective of this study was to determine the response of nitrifying bacteria present in the biofilm submitted to different aeration intensities during the production of Litopenaeus vannamei (Boone, 1931) in a clear water system and also with bioflocs. The study was composed of two experiments, where the first experiment was carried out without shrimp and consisted of four treatments with three replicates, in 800L tanks distributed in: 1) W/Air (control - without aeration); 2) V7.5 (flow rate 7.5 L/min); 3) V33.75 (flow rate of 33.75 L/min) and V75 (flow rate of 75 L/min. All treatments as artificial substrate, in the proportion of 200% of the lateral area of the tank. Experiment two was established after the results of the previous experiment, with three treatments and three replicates each: 1) BFT (biofloc, with flow rate of 20.00 L/min); 2) BFT+BF (biofloc and biofilm with flow rate of 33.75 L/min) and 3) BF (biofilm with flow rate of 33.75 L/min), in which the shrimp (7.89 ± 0.24g) were stored in nine tanks (800 L) with a density of 500 shrimps m-4.In both experiments Ammonia, nitrite were measured daily, while nitrate was analyzed weekly. The first experiment showed no difference in the ammonia concentrations of the different treatments, whereas nitrite showed higher concentrations in the treatment without aeration. The 33.75 L/min flow rate was chosen for experiment 2 to be compared with the aeration normally employed in our systems (20.00 L/min). In this last experiment, the nitrification process was more efficient in the treatments with biofilm and bigger air flow rate, with smaller concentrations of ammonia and nitrite in comparison to the BFT treatment. Similarly, treatments with biofilm and stronger flow rate showed better zootechnical performance of the shrimp.