The intensive shrimp culturing

The current applied intensive production methods in shrimp aquaculture systems tend to increase the carrying capacity for microbes, favouring the growth of opportunistic pathogens that can multiply rapidly (r-strategists). To reduce the risk of disease, the management of shrimp culture systems therefore aims to establish stable microbiota conditions, consisting of K-strategists (members of matured water) and probiotic bacteria. We investigated four different approaches to the intensive culturing of Litopenaeus vanamei post-larvae by setting up flow-though (FT), recirculation (RAS), heterotrophic biofloc (H-Floc) and autotrophic biofloc (A-Floc) systems. Over 30 days, we monitored water quality, shrimp growth and microbial indicators using culture-dependent quantification of heterotrophic bacteria, presumptive Vibrio spp. (≤ 104 CFU mL-1) and Bacillus spp., which were further classified into r- and K-strategists. We found a clear distinction between the RAS system and the other three culture systems in all measured parameters, with the RAS system producing the least shrimp growth, although the water was clear. However, shrimp growth was highest in heterotrophic biofloc systems; NO2-N concentration was highest at week 2. There was a shift from bacterial r-strategists to K-strategists after three weeks of culturing. Furthermore, the high abundance of beneficial strains of Bacillus suggested a stable, mature microbiota in the H-Floc system. Therefore, we propose that a stable microbiota consisting of beneficial probiotic bacteria, such as Bacillus spp. (≥ 104 CFU mL-1), and r-strategists (members of matured water) may protect shrimp from opportunistic pathogens and thereby prevent disease. The application of H-Floc system in shrimp aquaculture may offer a practical and effective solution to control harmful bacteria, although we recommend close monitoring during the first three weeks of culturing, as toxic NO2--N concentrations may develop and allow opportunistic pathogens to proliferate. The different approaches to water quality management had different bacterial compositions and rates of shrimp growth. Based on repeated measures correlation (rmcorr) analysis, pH was one of most important factors shaping microbial community structure in that pH was negatively correlated with Bacillus (r = -0.57, p = 0.019), K-strategists (r = -0.56, p = 0.02), TSS (r = -0.69, p < 0.001) and VSS (r = -0.64, p = 0.0019). Managing the water microbiome according to ecological r/K selection theory and pH stability (7.38 ± 0.13) may serve as a suitable approach for shrimp farmers to maintain productive shrimp culture and contribute to more sustainable shrimp aquaculture