Silymarin conserves the efficacy of quinolone and sulfonamide in Nile tilapia (Oreochromis niloticus) subjected to aflatoxicosis and Streptococcus agalactiae infection.

Aflatoxins (AFB) are adventitious plant toxins that act as immunosuppressants. Experimental Nile tilapia were divided into eight groups: AFB0 (control, uncontaminated diet), AFB50 (50 ppbAFB1), AFB100 (100 ppbAFB1), AFB150 (150 ppbAFB1), AFB0 + Sil (0 ppbAFB1+Sil), AFB50 + Sil (50 ppbAFB1+Sil), AFB100 + Sil (100 ppbAFB1+Sil), and AFB150 + Sil (150 ppbAFB1+Sil). The AFB1-residues in fish liver (AFB0, AFB50, AFB100, and AFB150) were 0.34, 0.54, and 0.82 ppb, respectively, while traces were recorded in muscles. Sil-supplemented fish had lower residues than other contaminated groups, which were still higher than AFB0. The gene expression of GPx, SOD, IL-1β, and TNF-α was significantly and linearly decreased with increasing aflatoxin levels, whereas Sil-supplementation (AFB50 + Sil) resulted in a high and significant increase of 3.86, 5.37, and 7.85 fold-change, respectively, compared with the fish groups and the control. While, CAT expression increased in response to a low aflatoxin level (AFB50; 2.17-fold-change), it decreased linearly with increasing aflatoxin level. Moreover, IL-10 expression was significantly higher in fish of AFB100 and AFB150, with 8.7- and 8.85-fold changes, respectively, compared to the control. Significant declines in immunoglobulin (Ig)M-2 and insulin-like growth factor (IGF) gene expression were observed in fish receiving AFB1-contaminated diets and Sil could enhance the expression. Innate immunity of the experimental fish was assessed by measuring the following parameters; serum antibacterial activity (SAB), oxidative burst activity (OBA), phagocytic activity (PA), phagocytic index (PI), and lysozyme (LYZ) as well as by challenge with Streptococcus agalactiae. Nile tilapia fed AFB1-contaminated diets showed immune-antioxidant suppressive status, indicating compromised health and a lowered survival rate (SR%) during bacterial challenge and antibiotic treatment Sil-supplementation could improve SR%.