Silybum marianum promotes growth, hepatic antioxidative activity, and splenic immunity but does not influence the intestinal barrier function of Nile tilapia, Oreochromis niloticus

Abstract

Alternative additives such as phytobiotics have been a research priority to promote chemotherapeutic-free and disease-resistant aquaculture. Hence, various Silybum marianum (SM) extract levels, including 1, 2, 3, and 4 g kg−1, were supplemented with a reference diet, and the reference diet containing no SM was considered a control. Each test diet was fed in triplicate to experimental fish for 60 days. The effects were observed on growth, liver, lymphoid organs (kidney and spleen), and intestinal health in relation to a panel of blood biochemical responses of Nile tilapia, Oreochromis niloticus. Better growth performance in Nile tilapia fed any supplementation levels of SM resulted from improved feed utilization and feed conversion ratio. Microscopic observations found normal kidney, liver, and spleen microstructure across all treatments. Of interest, the antioxidative capacity of the liver was stimulated by SM supplementation, supported by higher expression of CAT, SOD, and GPx genes coupled with higher levels of hepatic GST and T-AOC and lower levels of hepatic MDA concentrations. This was further aligned with lower levels of serum ALP, AST, and ALT relevant to liver function. Meanwhile, splenic immune relevant gene expression (IFN-γ1, LYZ, and hepcidin) increased significantly in all SM-treated fish compared to the control group. Also, hematological responses, including red blood cell indices (RBCs, Hb, HTC, PCV, MCV, MCH, and MCHC) and white blood cell indices (WBCs, lymphocytes, eosinophils, basophils, and heterophils), except monocytes, were improved by SM supplementation. Intestinal microstructures were normal, and their barrier functions were unchanged by dietary supplementation. Hence, SM extract could be used as a promising avenue for enhancing the functionality of aquadiet, leading to improving overall health performance. However, the mode of action of the bioactive ingredients present in SM extract is warranted to be further studied to consider SM as a functional additive for aquafeeds.