The application of probiotics for disease control in aquaculture is now a convincing approach towards replacement of antibiotics, which can cause adverse effects in aquatic animals and humans. In this study, we combined 2 probiotics, Lactobacillus acidophilus and Saccharomyces cerevisiae, with shrimp feed to create 2 formulas (WU8 and WU9), which were fed for 10 d to juvenile shrimp Penaeus vannamei. The shrimps were then subjected to a challenge infection with Vibrio parahaemolyticus, the causative agent of acute hepatopancreas necrosis disease (AHPND). The protective effects of probiotics against bacterial infection were investigated through histopathology of the hepatopancrease and immunological evaluation of shrimp. Both WU8 and WU9 probiotic mixtures (1:1, at 10⁸ and 10⁹ CFU kg diet^-1) increased blasenzellen hepatopancreatic epithelial cells and reduced pathology caused by AHPND. After 10 d of feeding, hemocyte parameters, including the total hemocyte count, percent of granular hemocytes, and phenoloxidase activity, increased significantly and were still increasing at 24 h post infection. Crustin and penaeidin 3 genes were also highly upregulated in hemocytes before and after 24 h of bacterial challenge and significantly upregulated in the hepatopancreas 1 to 5 d post-infection. A significantly higher survival rate was observed in shrimp fed with the probiotic supplemented diet (>90%) in comparison to the control group (60%). In conclusion, probiotic mixtures of L. acidophilus and S. cerevisiae reduced hepatopancreas pathology and protected shrimp from a challenge with AHPND.

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. Keywords: immune enhancement, lysozyme, marine diatoms, Penaeus vannamei, RNA interference, transcriptomics, Vibrio parahaemolyticus, β-glucan.

Background: Application of a virus-like particle (VLP) as a nanocontainer to encapsulate double stranded (ds)RNA to control viral infection in shrimp aquaculture has been extensively reported. In this study, we aimed at improving VLP’s encapsulation efficiency which should lead to a superior fighting weapon with disastrous viruses. Results: We constructed 2 variants of chimeric Macrobrachium rosenbergii nodavirus (MrNV)-like particles (V1- and V2-MrN-VLPs) and tested their efficiency to encapsulate VP37 double stranded RNA as well as WSSV protection in P. vannamei. Two types of short peptides, RNA-binding domain (RBD) and deca-arginine (10R) were successfully engineered into the interior surface of VLP, the site where the contact with VP37-dsRNA occurs. TEM and dynamic light scattering (DLS) analyses revealed that the chimeric VLPs remained their assembling property to be an icosahedral symmetric particle with a diameter of about 30 nm, similar to the original MrN-VLP particle. The superior encapsulation efficiency of VP37-dsRNA into V2-MrN-VLP was achieved, which was slightly better than that of V1-MrN-VLP but far better (1.4-fold) than its parental V0-MrN-VLP which the mole ratio of 7.5–10.5 for all VLP variants. The protection effect against challenging WSSV (as gauged from the level of VP37 gene and the remaining viral copy number in shrimp) was significantly improved in both V1- and V2-MrN-VLP compared with an original V0-MrN-VLP template. Conclusion: MrN-VLP (V0-) were re-engineered interiorly with RBD (V1-) and 10R (V2-) peptides which had an improved VP37-dsRNA encapsulation capability. The protection effect against WSSV infection through shrimp administration with dsRNA + V1-/V2-MrN VLPs was experimentally evident.