Galvanized materials induce oxidative stress in Cryptocaryon irritans by releasing zinc ions

Abstract

Mariculture fish often are infected with Cryptocaryon irritans, causing enormous losses to aquaculture. Our previous study indicated that galvanized materials showed good efficacy in controlling C. irritans infection. However, the toxic mechanism of galvanized materials on C. irritans is poorly understood. In this study, the mechanism of galvanized material toxicity on C. irritans was investigated, using seawater immersed with galvanized iron mesh (IGM seawater) and ZnSO4 solution. Furthermore, subcellular structural changes in C. irritans after treatment with zinc ions were determined. Finally, the content and function of reactive oxygen species (ROS) in the protomonts of C. irritans were assessed following treatment with zinc ions. The results showed that the parasite abundance in the IGM seawater group was significantly reduced compared with the control (P < 0.05). Furthermore, parasite abundance in the zinc ion-added groups (0.36 mg/L, 1.83 mg/L) which the zinc ions content was equal with IGM seawater group was significantly reduced compared with the control (P < 0.05). Zinc ions released from galvanized materials might be the most critical toxic agent to C. irritans. Additionally, deformation of mitochondrion was also found in the protomonts after treatment with zinc ions. The ROS content in protomonts of the Zn group was increased by 79.63% compared with the control group (P < 0.05). When the ROS were eliminated by an inhibitor, protomont mortality was decreased by 100% in the Zn group (P < 0.05). These results indicated that the toxic mechanism of galvanized materials to C. irritans may be from oxidative stress induced by releasing zinc ions.