Risk assessment and its control of synthetic antioxidant, Ethoxyquin, on immunity of farmed fish

乙氧基醌（EQ）已被用作家畜、水产养殖和宠物食品中的抗氧化剂。动物食品安全法规定动物饲料中EQ的上限为150 mg kg^（-1）。然而，水产养殖饲料中经批准的EQ水平（150 mg kg^(-1)）对鱼类健康的风险尚不清楚。本文研究了EQ对罗非鱼（Oreochromis niloticus）免疫的影响。在批准水平下，饲喂EQ的鱼血液中EQ的浓度达到0.16 mg kg^（-1）。该水平的EQ在体外抑制白细胞的吞噬活性，在体内抑制全血的抗菌活性。此外，在整个喂养过程中观察到肝脏固缩。然而，饲喂150 mg kg^(-1) EQ饲料30天后，死亡率无显著差异。虽然饲料中经批准水平的EQ会引起鱼类免疫抑制，但免疫抑制的严重程度并不会导致短饲养期的抗病性降低。

Ethoxyquin (EQ) has been used as an antioxidant in livestock, aquaculture and pet foods. Animal food safety law has established the upper limit of EQ in animal feed at 150 mg kg^(-1). However, the risk of EQ at the approved level for aquaculture feed (150 mg kg^(-1)) to fish health is unknown. Here, we examine the effect of EQ on the immunity of tilapia (Oreochromis niloticus). EQ concentration in the blood reached 0.16 mg kg^(-1) in fish fed EQ at the approved level. This level of EQ inhibited phagocytic activity of leucocytes in vitro and antibacterial activity of whole blood in vivo. Furthermore, pyknosis in the liver was observed throughout the duration of feeding. However, after 30 days of experimental challenge with feed containing 150 mg kg^(-1) EQ, no significant difference was observed in mortality. Although EQ at the approved level in feed causes immunity depression in fish, the severity of immune depression does not lead to a lowering of disease resistance for short feeding periods.