The growth promoting and immunomodulatory effects of a medicinal plant leaf extract obtained from Salvia officinalis and Lippia citriodora in gilthead seabream (Sparus aurata)

In the present study, we evaluated the effects of a medicinal plant leaf extract (MPLE; 10%, ursolic acid, 3% other triterpenic compounds; 2% verbascoside and < 1% polyphenols) obtained from Lippia citriodora and Salvia officinalis on somatic growth and immune responses in juvenile gilthead seabream (Sparus aurata). Fish (initial body weight = 26.0 ± 0.1 g) were fed two isoproteic (48% crude protein, 7% fishmeal), isolipidic (17% crude fat) and isoenergetic diets (21.7 MJ/kg), 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 (189.6 ± 2.5 g vs. 173.8 ± 4.1 g, respectively; P < 0.05). Specific growth rates (SGR) in fish fed the feed supplemented with 0.1% MPLE were significantly higher than in fish fed the control diet (SGR_{0–92 days (0.1% MPLE diet)} = 2.26 ± 0.01% day⁻¹, SGR_{0–92 days (control diet)} = 2.16 ± 0.02% day⁻¹; P < 0.05). Feed conversion ratio (FCR) values in fish fed the control diet were higher than those in fish fed the MPLE diet (FCR_{control diet} = 1.23 ± 0.02 vs. FCR _{0.1% MPLE diet} = 1.10 ± 0.02; P < 0.05). When evaluating non-specific immune plasmatic parameters, no significant variations were registered at the level of bacteriolytic and complement activities, nor protein IgM levels (P > 0.05). 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 h and the expression of genes associated to several immune processes was evaluated (humoral immune response, pro- and anti-inflammatory cytokines, cell surface markers, and antioxidant enzymes). Particularly at 4 h post-exposure, dietary supplementation with 0.1% MPLE enhanced SPCC immune response to LPS by the up-regulation of genes involved in humoral immunity (lys, IgM), pro- (tnf-α, il-1β) and anti-inflammatory (tgf-β1, il10) cytokines, the leucocyte cell surface marker cd4, and antioxidative stress enzymes (mn-sod, cat). Therefore, a medicinal plant leaf extract (MPLE) obtained from L. citriodora and S. officinalis may be considered as 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.