Enhancing Pacific white shrimp immunity against Vibrio parahaemolyticus through β-glucan supplementation from marine diatoms.

Background and aim: Pacific white shrimp (Penaeus vannamei) is a principal species in global aquaculture. However, outbreaks of Vibrio parahaemolyticus, the etiological agent of acute hepatopancreatic necrosis disease (AHPND), cause substantial economic losses. β-glucans derived from marine diatoms, Chaetoceros muelleri (CH) and Thalassiosira weissflogii (TH), have shown potential as immunostimulants to enhance shrimp resistance to pathogenic infections. This study aimed to evaluate the effects of β-glucans derived from CH, TH, and their combination on growth performance, immune responses, and survival of P. vannamei and to elucidate the underlying molecular mechanisms through transcriptomic and gene silencing approaches.

Materials and methods: Juvenile shrimp were assigned to four dietary groups for 30 days: Control (β-glucan-free), β-glucan from CH, TH, and a mixture of both (CH and TH) (CHTH). Growth performance, total hemocyte count (THC), and survival rate were evaluated. RNA-seq was performed on hepatopancreas samples after 14 days to identify differentially expressed genes (DEGs). Key immune-related DEGs were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Functional analysis of the lysozyme (Lyz) gene was conducted through RNA interference (RNAi), followed by V. parahaemolyticus challenge.

Results: The CHTH diet group exhibited significantly enhanced growth metrics and the highest survival rate. Transcriptomic analysis revealed 1,902 DEGs in the CHTH group compared to control, with 915 upregulated and 987 downregulated genes. qRT-PCR validated the expression trends of selected immune-related genes, notably Lyz, which showed robust upregulation. RNAi-mediated Lyz knockdown reduced survival upon bacterial challenge, confirming its role in β-glucan-induced immunity.

Conclusion: β-glucans derived from CH and TH, particularly in combination, significantly enhance growth performance and immunocompetence in P. vannamei. These findings underscore the potential of marine diatom-derived β-glucans as viable immunostimulants to mitigate AHPND in shrimp aquaculture, offering a sustainable alternative to antibiotic use.