Dose-dependent supplementation of Schizochytrium in the biofloc system modulates dual microbiomes to enhance growth and survival in Pacific white shrimp (Litopenaeus vannamei)
Integrating microalgae into biofloc system is a promising yet debated strategy in Pacific white shrimp (Litopenaeus vannamei) aquaculture, due to its inconsistent efficacy even for the same microalgal species. Such inconsistent performances are likely dose-dependent and the underlying microbial mechanisms remain elusive. Here, we investigated the impacts of supplementing microalga strain, Schizochytrium sp. ATCC 20888, at low (103 cells/mL, M1) and high (106 cells/mL, M2) levels compared with a clear water (CLW) system. Schizochytrium supplementation improved growth performance and feed efficiency and the M2 treatment further increased shrimp survival. Transcriptional profiling revealed the M2 treatment upregulated the expression of genes relevant to hepatopancreatic lipid and protein digestion (trypsin and lipase) and intestinal amino acid transportation (peptide transporter 1). Concurrently, M2 fortified the intestinal defense against pathogenic microbes by enhancing antimicrobial genes (lysozyme and penaeidin 3a). Redundancy analysis further supported the growth promotion was closely associated with improved lipid and a corresponding protein-sparing effect. Notably, Schizochytrium persisted at an extremely low abundance, whilst 16S rRNA sequencing revealed its disproportionate impact as a rare taxon on the microbiota in both biofloc and gut. High-dose supplementation enriched beneficial genera such as Aureispira, Marivita, Neptuniibacter, and Phaeodactylibacter in bioflocs, which are vital for nutrient recycling. Meanwhile, the intestinal microbiota was characterized by enrichment of the probiotic Fusibacter and the suppression of the opportunistic pathogen Shewanella. Overall, Schizochytrium orchestrates a dose-dependent reshaping of biofloc and gut microbiomes, effectively boosting the growth, feed efficiency, and specifically reinforcing antimicrobial activity of L. vannamei.