This study aimed to investigate the effects of dietary
selenium on resistance to skin haemorrhages and lesions and on immune function as well as the underlying mechanisms of those effects in the head kidney, spleen and skin of young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp with initial
body weight (226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of
selenium (0.025, 0.216, 0.387, 0.579, 0.795 and 1.049 mg/kg diet) for 80 days. After the feeding period, an immunization trial was performed by
infection with Aeromonas hydrophila for 14 days. The results showed that, compared with the optimal
selenium level, (1)
selenium deficiency impaired the production of antibacterial compounds and
immunoglobulins and down-regulated the transcript abundances of
antimicrobial peptides and
selenoproteins; (2)
selenium deficiency aggravated inflammatory responses in part by up-regulating pro-inflammatory
cytokines and down-regulating anti-inflammatory
cytokines mRNA levels, which were partially related to [IKKα, β, γ/IκBα/NF-κB] signalling and [TOR/(S6K1, 4E-BP1)] signalling, respectively. Interestingly,
selenium deficiency had no effect on the expression of TGF-β2, IL-4/13B,
IL-10,
IL-12p35,
IL-15 (skin only) or 4E-BP2 in the head kidney, spleen and skin of young grass carp. Finally, based on the percent
weight gain (PWG), the morbidity of skin haemorrhages and lesions, the ACP activity in the head kidney and the
lysozyme activity in spleen, the optimal dietary
selenium requirements for young grass carp were estimated to be 0.546-0.604 mg/kg diet. In summary,
selenium deficiency decreased the growth performance and impaired the immune function in the head kidney, spleen and skin of young grass carp.