The current study explores the hypothesis that low or excess levels of
lipids decrease the
enteritis resistance ability through impairing the intestinal physical and immune barrier function of young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp with an average initial weight of 261.41 ± 0.53 g were fed diets containing six graded levels of
lipids at 5.9, 21.4, 36.0, 50.2, 66.6 and 80.1 g/kg for 8 weeks. After that, a challenge trial was conducted by injection of Aeromonas hydrophila over 2 weeks. The results show that compared with optimal
lipids level, low or excess levels of
lipids impair fish immune barrier function through declining humoral compounds and down-regulating the
mRNA levels of
interleukin 4/13A (IL-4(13)A) [not in the proximal intestine (PI)], IL-4(13)B,
IL-6,
IL-10,
transforming growth factor β1 (TGF-β1), inhibitor of κBα (IκBα), TOR and ribosomal p70S6
kinase (S6K1) (P < 0.05), and up-regulating
tumor necrosis factor α (TNF-α),
interferon γ2 (IFN-γ2), IL-1β,
IL-8,
IL-12 p40 (not p35), nuclear factor κB p65 (NF-κB p65), IκB
kinase α (IKKα), IKKβ, IKKγ, and eIF4E-binding
protein (4EBP) in the intestine of young grass carp (P < 0.05). In addition, low or excess levels of
lipids also decrease young grass carp physical barrier function through down-regulating the
mRNA levels of zonula occludens (ZO-1), ZO-2b [only in the distal intestine (DI)],
Claudin b, c, 3, 12, 15a, 15b (only in the DI), 7b (not 7a) and
Occludin by
MAPKK 6/
p38 MAPK (not JNK)/MLCK signaling molecules, down-regulating B-cell lymphoma-2 (Bcl-2) and
inhibitor of apoptosis protein (IAP) and up-regulating the
mRNA levels of apoptotic
protease activating factor-1 (Apaf-1),
Caspase-3, -8 and -9 and
Fas ligand (FasL) (not in the DI), and decreasing
antioxidant ability via Kelch-like ECH-associating
protein 1 (Keap1)/
NF-E2-related factor 2 (Nrf2) signaling molecules in the intestine. Based on the quadratic regression analysis for the
enteritis resistance ability, LA activities and GSH content in the MI were established to be 54.5, 49.91 and 47.83 g
lipid/kg diets, respectively.