Cadmium (Cd) is a ubiquitous environmental contaminant, posing serious threats to aquatic organisms. The aims of the present study were to investigate the effects of long-term Cd exposure on the growth, GH/IGF axis, antioxidant defense and DNA methylation in juvenile Nile tilapia (Oreochromis niloticus). To this end, juvenile Nile tilapia were exposed to 0, 10 and 50 µg∙L⁻¹ Cd for 45 and 90 days. The obtained results revealed that exposure to high concentrations of Cd significantly decreased body mass and body length, and down-regulated mRNA levels of GHRs, IGF-I and IGF-II in the liver of Nile tilapia. Cd exposure induced oxidative stress including the reduction of antioxidant activities and increases of malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG) contents. Beside, the global DNA methylation levels significantly decreased with increasing Cd concentration and exposure time, which might result from increased oxidative DNA damage, the down-regulated expression of DNMT3a and DNMT3b and up-regulated expression of TET1 and TET2. In conclusion, long-term Cd exposure could inhibit growth, reduce antioxidant capacity and lead to oxidative damages to lipid and DNA, and decrease global DNA methylation level in juvenile Nile tilapia.

镉 (Cd) 是一种普遍存在的环境污染物，对水生生物构成严重威胁。本研究的目的是研究长期 Cd 暴露对尼罗罗非鱼 ( Oreochromis niloticus )幼鱼生长、GH/IGF 轴、抗氧化防御和 DNA 甲基化的影响。为此，将尼罗罗非鱼幼鱼暴露于 0、10 和 50 µg∙L ^-1 Cd 45 和 90 天。获得的结果表明，暴露于高浓度 Cd 显着降低体重和体长，并下调GHR、IGF-I和IGF-II 的mRNA 水平在尼罗罗非鱼的肝脏中。镉暴露诱导氧化应激，包括抗氧化活性的降低和丙二醛 (MDA) 和 8-羟基脱氧鸟苷 (8-OHdG) 含量的增加。此外，整体 DNA 甲基化水平随着 Cd 浓度和暴露时间的增加而显着降低，这可能是由于氧化性 DNA 损伤增加、DNMT3a和DNMT3b表达下调以及TET1和TET2表达上调所致。总之，长期接触镉会抑制尼罗罗非鱼的生长，降低抗氧化能力并导致脂质和DNA的氧化损伤，并降低整体DNA甲基化水平。