Aquaculture is the fastest-growing food-production sector and as the intensification of production increases, so do diseases. Increased public concern about antibiotic resistance has led to the search for alternative solutions to reduce the impact of diseases in the farm output. Medicinal plants, rich in secondary metabolites and phytochemical compounds, are an interesting alternative to prevent diseases in aquaculture.
A group of Spanish and Chilean researchers evaluated the effects of a medicinal plant leaf extract (MPLE; 10%, ursolic acid, 3% other triterpenic compounds; 2% verbascoside and < 1% polyphenols; Natac Biotech) obtained from Lippia citriodora and Salvia officinalis on somatic growth and immune responses in juvenile gilthead seabream (Sparus aurata). Fish were fed two isoproteic, isolipidic and isoenergetic diets, one of them containing 0.1% MPLE. Both diets were tested using four replicate tanks during 92 days.
At the end of the trial, a significant increase in growth was observed in fish fed the diet containing the additive in comparison to fish fed the control diet. Specific growth rates (SGR) in fish fed the feed supplemented with 0.1% MPLE were significantly higher than in fish fed the control diet. Feed conversion ratio (FCR) values in fish fed the control diet were higher than those in fish fed the MPLE diet. When evaluating non-specific immune plasmatic parameters, no significant variations were registered at the level of bacteriolytic and complement activities, nor IgM levels.
In order to evaluate the cellular immune competence of fish, an ex vivo assay with splenocytes primary cell culture (SPCC) from both dietary groups was conducted. SPCC were incubated with lipopolysaccharide (LPS) for 24 hours and the expression of genes associated with several immune processes was evaluated (humoral immune response, pro- and anti-inflammatory cytokines, cell surface markers, and antioxidant enzymes). Particularly, at four-hours post-exposure, dietary supplementation with 0.1% MPLE enhanced SPCC immune response to LPS by the up-regulation of genes involved in humoral immunity, pro- and anti-inflammatory cytokines, the leucocyte cell surface marker cd4, and antioxidative stress enzymes.
Researchers suggest that a medicinal plant leaf extract obtained from L. citriodora and S. officinalis may be considered as an efficient additive to be used in aquafeed since it does not induce a significant immune reaction under basal conditions, but it provides immune protection after LPS treatment, together with increasing overall fish growth and improvement of feed efficiency values.
Check out the study here.