In this study, the protective effects and potential mechanisms of (2-Carboxyethyl) dimethylsulfonium
Bromide (Br-
DMPT) were evaluated in relation to the gill health status of on-growing young grass carp (Ctenopharyngodon idella). A total of 450 grass carp (216.49 ± 0.29 g) were randomly distributed into five treatments of three replicates each (30 fish per replicate) and were fed diets supplemented with gradational Br-
DMPT (0-520.0 mg/kg levels) for 60 days. Subsequently, the fish were challenged with Flavobacterium columnare for 3 days, and the gills were sampled to evaluate
antioxidant status and immune responses evaluation. Our results showed that, when compared to the control group, dietary supplementation with appropriate Br-
DMPT levels resulted in the following: (1) decreased gill rot morbidity and improved gill histological symptoms after exposure to F. columnare (P < 0.05); (2) improved activities and gene expression levels (except GSTP2 gene) of
antioxidant enzymes and decreased oxidative damage parameter values (
reactive oxygen species,
malondialdehyde and
protein carbonyl) (P < 0.05), which may be partially associated with the nuclear factor-erythroid 2-related factor 2 (Nrf2) signalling pathway (P < 0.05); (3) increased
lysozyme (LZ) and
acid phosphatase (ACP) activities and
complement 3 (C3), C4 and
immunoglobulin M (
IgM) contents, and upregulated genes expressions of antibacterial
peptides (
liver-expressed antimicrobial peptide-2A, -2B,
hepcidin, β-
defensin and mucin2) (P < 0.05); (4) upregulated gene expressions of anti-inflammatory
cytokines (except IL--4/13B) that may be partially to the TOR/(S6K1, 4E-BP1) signalling pathway, and downregulated gene expressions of pro-inflammatory
cytokines (except IL-12P35) may be partially to the IKK β, γ/IκBα/
NF-kB) signalling pathway (P < 0.05). Taken together, our results indicate that dietary supplementation with appropriate amounts of Br-
DMPT may effectively protect on-growing grass carp from F. columnare by strengthening gill
antioxidant capacity and immunity. Furthermore, based on measures of combatting gill rot,
antioxidant indices (MDA) and immune indices (LZ), the dietary Br-
DMPT supplementation levels for on-growing grass carp are recommended to be 291.14, 303.38 and 312.01 mg/kg diet, respectively.