Salmon Rickettsial Septicemia (SRS), caused by Piscirickettsia salmonis, is one of the main bacterial diseases in Chilean salmon farming. It generates high mortality rates and production losses, which has driven the search for more sustainable therapeutic alternatives.
This study evaluated the efficacy of a broad-spectrum natural botanical formulation designed to inhibit bacterial growth through multiple mechanisms: disruption of quorum sensing signaling, alteration of membrane integrity, and inhibition of protein and nucleic acid synthesis. In addition, it sought to enhance the fish’s immune defenses, as well as reduce inflammation and oxidative stress.
The trials were carried out in farming centers in southern Chile. Groups of Salmo salar were fed the formulation for 30 days and then challenged with Piscirickettsia salmonis (strains LF-89 and EM-90) for another 30 days. Mortality rates, prevalence of infection, and physiological, histological and molecular analyses were carried out.
The treated fish showed a 64% reduction in infectious mortality compared to the control group. Significant activation of immune markers related to salmon rickettsial septicaemia (SRS), including CD4, CD8, IFN-γ, TNF, IL-1β, IL-10, lysozyme, and transferrin, was evidenced, indicating a potentiated adaptive immune response. Likewise, a decrease in oxidative stress was observed, reflected in lower activity of antioxidant enzymes in NFEL2, SOD3, CAT, GPX markers and in the reduction of the expression of genes associated with epithelial damage in the intestine, skin and gills, reflected by MMP2, MMP13, COL1A1.
From the histological point of view, the treated fish had higher intestinal villi height, less inflammation in enteric mucosa and greater density of mucosal cells in the skin, which suggests an improvement in the absorption capacity and in the barrier function against external agents (pathogens and inflammatory). In addition, a significant decrease in the general histopathological score was observed, with marked reductions in the levels of necrosis, inflammatory infiltration, and tissue damage, especially in the liver, kidney, and spleen.
Positive differences were observed in terms of production parameters, such as a 17% increase in growth and -7% FCR (feed conversion rate).
Taken together, these findings support the use of this botanical formulation as an effective and sustainable strategy for the management of Piscirickettsia salmonis. Its use significantly reduces mortality and strengthens the overall health of the fish, while minimizing the need for antibiotics and the associated risk of antimicrobial resistance in salmon farming.