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Background: Shrimp gill health is an indicator of their overall health and environmental stress, as gills are in direct contact with the external environment. Organic selenium (OS), known for its high bioavailability and antioxidant properties, potentially enhances shrimp growth, survival, and immune responses. This study investigated the physiological features through comprehensive gill gene expression profiling and growth parameters by incorporating OS into Penaeus vannamei diets. Methods and results: Two OS-containing products, AlkoSel (AS) and SelPlex (SL), were supplied to the diet of P. vannamei (0.90 ± 0.05 g body weight, 4.54 ± 0.5 cm length) at a dose of 0.4 mg Se kg− 1 ration in the final feed. Three groups were organized: an AS-fed group, an SL-fed group, and a control (C) group without additives. After a one-month feeding trial, performance indices (PI) were assessed and RNA-Seq analysis was conducted. The PI revealed that both OS products had similar growth-stimulating effects, with no significant differences between the two groups. However, both groups showed significant improvement compared to the C-group. The P. vannamei gill transcriptome was strongly impacted by the two OS products, with several KEGG pathways implicated in their metabolic mechanisms. Pathways related to energy metabolism, carbohydrate metabolism, lipid metabolism, non-specific immunity, and antioxidative responses were significant in regulating the addition of AS and SL to P. vannamei diets. Conclusions: While SL had some higher additive effects on the gene expression profile than AS, OS from either product is an essential micronutrient that promotes growth, normal metabolic activities, and good gill health in P. vannamei during the early feeding period. [ABSTRACT FROM AUTHOR]

Asian seabass (Lates calcarifer) is an economically important fish species that is widely cultivated in Thailand. However, aquaculture of Asian seabass is limited by infectious diseases. One of the most serious diseases is photobacteriosis, caused by Photobacterium damselae. Vaccination is recognized as an efficient disease prevention and pathogen control method for strengthening the aquaculture industry. To promote vaccine development, the characterization of pathogenic bacteria and their pathogenesis is required. In this study, isolates of P. damselae were obtained from commercial aquaculture farms in Thailand during 2019–2021. Analyses of 16S rRNA and the urease subunit alpha genes identified the isolates as P. damselae subsp. damselae (Phdd). Antibiotic susceptibility analyses showed that all Phdd isolates were resistant to amoxicillin (10 μg). Haemolysis and phospholipase activities were used to categorize P. damselae into three groups based on their biological activities. The pathogenicity of four candidates (SK136, PD001, PD002 and T11L) was tested in Asian seabass. Isolate SK136 showed the highest virulence, with a lethal dose (LD50) of 1.47 × 105 CFU/fish, whereas isolate PD001 did not show any virulence. Genotypic characterization, based on multi‐locus sequence typing analysis, demonstrated that all candidates were novel strains with new sequence types (64, 65, 66 and 67). Preliminary vaccination using formalin‐killed cells (FKCs) protected Asian seabass from artificial challenges. Taken together, these results provide fundamental knowledge for vaccine development against Phdd infection in Asian seabass. [ABSTRACT FROM AUTHOR]

Aims This study aimed to assess the effects of chlorine dioxide (ClO2) in water on whiteleg shrimp Penaeus vannamei , evaluating its impact on the stomach microbiota, gill transcriptome, and pathogens. Methods and results ClO2 was added to the aquarium tanks containing the shrimp. The application of ClO2 to rearing water was lethal to shrimp at concentrations above 1.2 ppm. On the other hand, most of the shrimp survived at 1.0 ppm of ClO2. Microbiome analysis showed that ClO2 administration at 1.0 ppm significantly reduced the α-diversity of bacterial community composition in the shrimp stomach, and this condition persisted for at least 7 days. Transcriptome analysis of shrimp gill revealed that ClO2 treatment caused massive change of the gene expression profile, including stress response genes. However, after 7 days of the treatment, the gene expression profile was similar to that of shrimp in the untreated control group, suggesting a recovery to the normal state. This 1.0-ppm ClO2 significantly reduced shrimp mortality in artificial challenges with an acute hepatopancreatic necrosis disease-causing Vibrio parahaemolyticus and white spot syndrome virus, which were added to rearing water. Conclusions The use of ClO2 at appropriate concentrations effectively eliminates a significant portion of the bacteria in the shrimp stomach and pathogens in the water. The results of this study provide fundamental knowledge on the disinfection of pathogens in water using ClO2 and the creation of semi germ-free shrimp, which has significantly decreased microbiome in the stomach. [ABSTRACT FROM AUTHOR]