Antiparasitic Effect of Copper Alloy Surface on Cryptocaryon irritans in Aquaculture of Larimichthys crocea

Copper and alloys containing >60% copper by weight are antimicrobial. In aquaculture, copper alloys are used as part of corrosion-resistant cages or as part of copper coating. To test whether a copper alloy surface prevents the outbreak of parasitosis in the aquaculture of , we covered the bottom of the aquaculture tank with sheets of copper alloy containing 74% to 78% copper, and we cultured juveniles that had been artificially infected with the protozoan parasite Our results showed that these copper alloy sheets effectively blocked the infectious cycle of within a 1-week period and significantly reduced the number of trophonts and tomonts, thereby decreasing the mortality rate of In assays, the cytoplasmic membranes of protomonts disintegrated and the cytoplasm overflowed after just 5 minutes of contact with copper alloy surfaces. Although the same cytoplasmic membrane disintegration was not observed in tomonts, the tomonts completely lost their capacity for proliferation and eventually died following direct contact with copper alloy sheets for 1 h; this is likely because tomonts took in >100 times more copper ions following contact with the copper alloy sheets than within the control aquaculture environment. Exposure to copper alloy sheets did not lead to excessive heavy metal levels in the aquacultured fish or in the culture seawater. , a parasitic ciliate that penetrates the epithelium of the gills, skin, and fins of marine fish, causes acute suffocation and death in cultured fish within days of infection. Much of the existing research centers around the prevention of infection, but no cure has been found. Studies demonstrate that copper has strong antimicrobial properties, and fish grown in copper-containing cages have lower rates of infection, compared to those grown in other currently used aquaculture cages. In this study, we found that an alloy containing 74% to 78% copper by weight effectively killed cells and prevented cryptocaryoniasis outbreaks within a 1-week period. These findings offer a new perspective on the prevention and control of cryptocaryoniasis.