Aquaculture emerges as the fastest-growing sector in animal production, yet it grapples with significant challenges, particularly disease outbreaks which pose formidable obstacles for numerous aquatic species. A considerable amount of attention is thus directed towards substances exhibiting antibacterial properties, essential for bolstering disease resistance and promoting sustainable aquaculture practices. In this study, the impact of incorporating a thymol-based Botanical Blend Formula (BBF), previously validated in vitro against Piscirickettsia salmonis, on the modulation of genes governing cellular-mediated immunity in Atlantic salmon ( Salmo salar) is evaluated.
One hundred and eighty-nine Atlantic salmon specimens, with a mean weight of 14g, were randomly assigned to 9 tanks (21 fish per tank) at Universidad Católica de Temuco in Chile. Three distinct diets were administered in triplicate: i ) Control, ii) D2 (BBF 1000ppm), and iii) D3 (BBF 2000ppm). Over a period of 43 days, the fish were fed until they doubled in size. Following a 48-hour fasting period, fish selected for tissue sampling were randomly chosen and euthanized using a lethal dose of anesthetic (BZ-20). Six individuals per tank were utilized to obtain anterior kidney samples, which were subsequently dispatched to Universidad Austral de Chile. The transcript levels of il-1β, il-8, and cd8 were then analyzed using RT-qPCR.%.
Graphs depict the expression levels for each diet as the average ± SEM (n=18), relative to the control diet, calculated using the ΔΔCt method with the ef-1α transcript serving as a normalizer. Asterisks highlight statistically significant differences in expression levels relative to the control diet, determined through one-way ANOVA followed by Dunnett’s multiple comparisons test (p-value<0.05).
In conclusion, the results indicate that D3 positively modulated markers of immunity, resulting in elevated levels of il-1β and cd8. Although D2 significantly influenced il-8 transcription, it also displayed favourable trends across all analyses. Both diets demonstrated immune-stimulating properties, particularly in enhancing cellular-mediated immunity, suggesting potential for a faster and more efficient response against pathogens.