A team of Spanish researchers evaluated the effect on the health of two relevant mucosal tissues, skin and intestine, of a feed additive composed of essential oils of garlic, carvacrol and thymol in seabream.
“Results show that these essential oils have a stimulating effect on specific immunity in the skin and modulation of the immune response in the intestine, reinforcing a previous study in which we saw their protective effect on gills parasitized by Sparicotyle chrysophrii,” said Enric Gisbert, head of the Aquaculture Program at IRTA.
The enrichment analysis of the skin transcriptional profile of the skin showed a positive regulation of genes associated with cellular components of the secretory pathway, suggesting the stimulation and recruitment of cells with phagocytic capacity. On the other hand, several genes known for their participation in the nonspecific immune response were identified.
Results of an in vitro challenge supported the transcriptomic results obtained in the nutritional test, where a significant reduction in the growth of Vibrio anguillarum and Pseudomona anguilliseptica was observed in the epidermal mucus of fish fed with the additive, suggesting a secretion promotion of humoral immune factors in the mucus by the additive. Stress parameters, such as cortisol, were also significantly decreased in the epidermal mucus of seabream fed with the additive.
At the intestinal level, the transcriptomic analysis showed similar results to those observed in a previous study in gills, with the modulation of inflammatory processes, immunity associated with granulocytes, transport and secretion, as well as response processes to cyclic compounds and symbiosis. Although the diversity indices of the intestinal microbiota were not affected by the additive, it did promote subtle changes in the abundance of certain phyla, classes and genera. Additionally, the study of the functionality of the microbiota showed an increase in bacterial sequences associated with glutathione and lipid metabolism. Based on the set of results, it has been hypothesized that these alterations in the microbial composition of the intestine and its functionality actively participate in the modulation of the observed transcriptomic profile, and vice versa, probably because of the immunostimulatory effect of the additive results from its impact on the host-microbiota co-metabolism.
“These results suggest that the microencapsulation of garlic essential oil, carvacrol and thymol could be considered a sustainable immunostimulating dietary strategy with antimicrobial properties against specific fish pathogens, which would improve stress parameters without compromising the intestinal health of farmed fish,” said the IRTA researcher.
This work has been carried out within the framework of the DIETAplus project, funded by JACUMAR of the Ministry of Agriculture, Fisheries and Food and the European Maritime and Fisheries Fund (FEMP), and by the Doctorats Industrials program (Generalitat de Catalunya; TECNOVIT- PHARMFAES).
Download the skin study and the intestinal study.
