Rearing of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) in BFT system with different photoperiods: Effects on the microbial community, water quality and zootechnical performance

In Biofloc Technology (BFT) Systems, there are changes in microbial communities during a shrimp culture cycle; usually, heterotrophic bacteria are replaced by a photoautotrophic or chemoautotrophic community, depending on the management employed. When the water is exposed to sunlight, it can abruptly change from a heterotrophic system (dominated by bacteria and protozoa) to a predominantly photoautotrophic system, with a dominance of microalgae. However, there is little information on the characterization and quantification of the microbial community in the culture of the Pacific white shrimp Litopenaeus vannamei in a BFT system with light restriction, especially the contribution of these microrganisms to the zootechnical performance of shrimp. The aim of this study was to evaluate the microbial community in a rearing environment with light restriction. The study was conducted in 12 tanks (800 L) with a storage density of 500 shrimp m(-3) and an initial shrimp weight of 0.053 g. The experiment was designed with three treatments and four replicates distributed into the following groups: i) natural photoperiod - 12 h light/12 h dark (NP); ii) 24 h light (24hLI); and iii) 24 h dark (24hDA). Significant differences were found in water quality parameters (lower values of ammonia and nitrite in the 24hDA treatment), and higher values of CO2, light (Ix) and chlorophyll were observed for the NP and 24hLI treatments than for the 24hDA treatment (p < .05). Zootechnical performance registered higher values in final weight, final biomass, weekly growth rate and survival in the NP and 24hLI treatments than in the 24hDA treatment (p < .05). Proximal analysis of the biofloc showed higher concentrations of proteins and lipids in the NP and 24hLI treatments than in the 24hDA treatment (p < .05), and there was a greater abundance of bacteria (attached coccoid, free filamentous, and attached filamentous bacteria, Vibrio and Bacillus) in NP and 24hLI than in 24hDA (p < .05). There was a greater abundance of photoautotrophic flagellates, heterotrophic flagellates, ciliates, dinoflagellates, rotifers and nematodes in NP and 24hLI than in 24hDA (p < .05). The results show that light restriction favored nitrification. However, light exposition promoted an increased abundance of microrganisms, providing an additional food source and reflecting a lower rate of feed conversion, higher survival and better growth performance for L. vannamei.