Detalle de: Biofilm microbial succession in recirculating aquaculture systems as response to diet input and water refreshment

Biofilm formation in nitrifying biofilters is well studied within recirculating aquaculture systems (RAS), while tank biofilms are often neglected and remain largely unexplored. Detached biofilms can facilitate microbial transfer through recirculating water; thus, understanding the succession of these communities is highly relevant for effective RAS operation. Furthermore, tank biofilms are directly affected by nutrient composition and concentrations in the water, which are driven by fish waste excretions and specific diet formulations. Therefore, this study investigated how fish diet composition and water refreshment strategies alter the temporal dynamics of tank biofilms across different aquaculture systems. Three mariculture systems with varying water refreshment levels, stocked with gilthead seabream, were examined: a flow-through system (FTS), a high refreshment system (HR-RAS), and a low refreshment RAS (LR-RAS). The fish were fed two contrasting diets, specifically a fibre-rich or a starch-rich diet, over an eight-week period. Water quality, nutrient concentrations, and biofilm development were analyzed at the tank level at weeks 0, 2, 5, and 8. Tank biofilms in the LR-RAS exhibited the highest microbial abundance, as measured by qPCR, alongside elevated levels of all nutrients, indicating that nutrient accumulation significantly promotes biofilm growth. Microbial communities shifted over time across all systems, developing distinct profiles driven by physicochemical water quality parameters. Diet also influenced biofilm community composition, most evidently in the LR-RAS. This first reported study on tank biofilm communities within RAS demonstrates that system-driven environmental conditions primarily determine biofilm growth and composition, while diet exerts supplementary influence strictly under low water refreshment conditions.