Different management strategies for artificial substrates on nitrification, microbial composition, and growth of Penaeus vannamei in a super-intensive biofloc system

Abstract

The aim of this study was to test the effect of different management strategies for artificial substrates on the nitrification process, microbial composition of water and biofilm, and growth of Penaeus vannamei in a super-intensive biofloc system. The research was conducted over 60 days using experimental units of 200 L and had the following treatments: T1 – artificial substrate + biofloc + shrimp + aeration (control), T2 - artificial substrate + water + aeration, T3 - artificial substrate + water, and T4 - only artificial substrate. The experiment was divided into two phases. Phase 1 involved maintaining the artificial substrates under the management strategy for 30 days. Phase 2 involved the use of substrates from phase 1 in a shrimp nursery for 30 days. Pre colonized artificial substrates (Needlona®) were employed at a ratio of 200 % of the tank's lateral area to promote biofilm growth. In the phase 1, T1 used a stocking density of 500 shrimp m−3 (9.72 ± 0.50 g). In phase 2, shrimp weighing 0.10 ± 0.05 g were stocked at a density of 1750 shrimp m−3 and all treatments included artificial substrates from phase 1, aeration, water, and shrimp. Molasses was the carbon source organic used. In phase 2, ammonia control was observed in treatments T2, T3, and T4 from the 10th day onwards. T4 had a nitrite spike, controlled from day 14 onwards, suggesting recovery of the nitrifying bacteria community. At the end of the phase 2, T2 and T4 showed higher abundance of coccoid bacteria in the biofilm compared to T1 and T3. T4 also had more bacillus. The shrimp final weight was higher in T2 compared to the other treatments. These findings suggest that maintaining the substrate submerged in water (T3) can be considered a practical management for artificial substrates and that it does not limit the nitrification process between culture cycles. Furthermore, exposure of artificial substrates to air (T4) also did not affect the nitrification process, leading to the recovery of the bacterial community, and the proliferation of various bacterial groups.