Abstract
In aquaculture, maintaining optimal fish health and welfare is one of the main challenges, primarily due to multiple stressors including high stocking densities, temperature fluctuations, jellyfish blooms, or pathogenic diseases. Among these, infectious diseases notably impact fish survival and overall welfare, leading to significant economic losses. An innovative approach to mitigate these effects and enhance aquaculture sustainability involves incorporating functional feed additives into fish diets.
In recent years, numerous functional feed additives such as probiotics, prebiotics, nucleotides, single-cell proteins, and phytochemicals have been integrated into aquaculture feeds to enhance fish robustness under stressful conditions. Notably, whole plant materials, owing to their phytochemical complexity, have emerged as promising ingredients with potential health benefits.
In this context, we evaluated the immunomodulatory effects of a specific plant material in fish, using both in vitro and in vivo approaches. Initially, we performed a series of in vitro experiments employing rainbow trout cell lines (RTS11 and RT-gut) and primary head kidney leukocyte cultures. Here, we examined the expression of inflammatory biomarkers following stimulation with Aeromonas salmonicida in the presence of the plant extract. The results indicated a significant reduction in the expression of pro-inflammatory genes, including il1β, tnf-α, and saa5. Additionally, flow cytometry analyses revealed a decrease in phagocytic capacity of RTS11 cells, and reduced IgM secretion by B cells in primary cultures. These outcomes suggest differential immunomodulatory effects depending on cell type and the concentration of plant material.
Encouraged by these findings, we subsequently formulated an experimental diet incorporating the tested plant material combined with other functional ingredients, aiming to evaluate potential synergistic effects. Two in vivo challenge trials were conducted, involving bacterial (Yersinia ruckeri) and viral (viral hemorrhagic septicemia virus) pathogens. Remarkably, fish fed with the experimental health-promoting diet showed significantly increased survival rates compared to those fed a control diet or a similar diet without the plant additive.
Collectively, these findings demonstrate that this novel plant additive exhibits promising anti-inflammatory properties and potential synergy with other functional ingredients, making it a valuable addition to functional diets aimed at improving fish health and resilience in aquaculture systems.