Probiotic complexity dictates growth performance, physiological status, and water quality of super-intensive Pacific white shrimp (Litopenaeus vannamei) biofloc system

Abstract

Supplementing biofloc systems with functionally specialized probiotics represents a promising strategy for super-intensive Pacific white shrimp (Litopenaeus vannamei) aquaculture. Nevertheless, the efficacy and the microbial mechanism are still opaque. Based on heterotrophic nitrifying bacterium Providencia rettgeri (N), which has exhibited holistically promoting effects to the shrimp biofloc system, we further compared the impacts (N) with a dual consortium (N + Bacillus subtilis; NB) and a triple consortium (NB + effective microorganisms; NBE). Our results demonstrated that survival rates from all groups exceeded 76% with no significant differences. Regarding growth performance, NB simultaneously promoted the growth speed and the feed utilization of shrimp, whilst NBE exerted negative effects on feed efficiency. Besides, NB consortium kept the lowest inorganic nitrogen in the rearing water. Microbiome profiling of biofloc revealed NB induced a distinct microbial structure, characterized by nitrifying bacteria (e.g., Nitrosomonas) and intestinal symbionts (e.g., Candidatus Bacilloplasma). Physiologically, shrimp reared in NB showed higher catalase activity. In contrast, NBE suppressed superoxide dismutase activity and induced compensatory transcription of digestion (trypsin and lipase) and lipid metabolism (peroxisome proliferator-activated receptor γ). Transcriptomic analyses further elucidated, in comparison with N, NB stimulated host energy metabolism via the TCA cycle and glycolysis, whereas NBE triggered cellular stress and macromolecular catabolism, notably enriching autophagy and ubiquitin-mediated proteolysis pathways. In conclusion, the combination of P. rettgeri and B. subtilis synergistically optimizes the output and ecology to the super-intensive L. vannamei biofloc system. Excessive microbial complexity results in a metabolic burden, forcing the host to prioritize stress responses instead of growth. Further work should concentrate on optimizing probiotic formulas in which prioritize ecological compatibility over mere strain richness.