Copper alloy particles incorporated in coatings improve the surfaces of aquaculture tanks for controlling Cryptocaryon irritans infections

Abstract

Previous studies have found that copper alloy sheets can kill the protozoan Cryptocaryon irritans effectively as the tomonts of this particular pathogen adhere to the hard surface of tanks. This study explored the potential use of copper alloy particles incorporated into coatings to be applied to the bottom of aquaculture tanks, in order to control cryptocaryoniasis outbreaks. Results showed that the number of trophonts on Trachinotus ovatus exposed to such copper coated surfaces was significantly lower than that in the control and blank groups 5 days later and effectively blocked the reinfection of C. irritans, thereby decreasing the mortality rate of T. ovatus. In in vitro assays, the mortality rate of protomonts and tomonts was up to 100% at 6th h and 24th h of post contacting with the copper coated surfaces, respectively. Safety assessments found that copper concentration was not significantly high in flowing seawater, but it showed an upward trend with longer immersion time, increasing significantly from 0.56 to 5.90 μg/L within a 30-day period. When exposed to the copper alloy coating, the bottom-crawling fish Epinephelus coioides, did not accumulate an excessive copper concentration in the serum, liver or muscle tissues. This study provides a safe and effective strategy to control cryptocaryoniasis in marine factory farming.