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 Larimichthys crocea, we covered the bottom of the aquaculture tank with sheets of copper alloy containing 74% to 78% copper, and we cultured L. crocea juveniles that had been artificially infected with the protozoan parasite Cryptocaryon irritans Our results showed that these copper alloy sheets effectively blocked the infectious cycle of C. irritans within a 1-week period and significantly reduced the number of C. irritans trophonts and tomonts, thereby decreasing the mortality rate of L. crocea In in vitro 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 C. irritans 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.IMPORTANCECryptocaryon irritans, 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 C. irritans 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 C. irritans 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 C. irritans cells and prevented cryptocaryoniasis outbreaks within a 1-week period. These findings offer a new perspective on the prevention and control of cryptocaryoniasis.

Food intake, survival, and immunity of Nibea albiflora to Cryptocaryon irritans infection.

Cultured Nibea albiflora rarely die from cryptocaryoniasis. To explore the resistance of N. albiflora against the invasion of Cryptocaryon irritans, in this study, 40 g N. albiflora was artificially infected with C. irritans at a median lethal concentration (2050 theronts/g fish). The food intake, survival, relative infection intensity, and immobilization titer variation of serum and mucus at different time points after the infection were compared. Results showed that the ingestion of N. albiflora could be resumed only 1 day after feed deprivation by the disease, which indicated the quick resilience of N. albiflora. N. albiflora did not die out even if it was cultured continually for up to 15 days at 27 °C in a culture tank with a large quantity of C. irritans tomonts. It was because that, without any exterior force, N. albiflora could block the C. irritans cell proliferation, and then the pathogens disappear gradually. In vitro immobilization titer test results confirmed that the serum and mucus could directly eradicate C. irritans.

Comparison of the susceptibility and resistance of four marine perciform fishes to Cryptocaryon irritans infection.

Cryptocaryon irritans is a type of marine ectoparasitic ciliate that infects teleost fishes. To illustrate the susceptibility and innate immune mechanism of fishes to C. irritans, four species of marine perciform fishes were selected in Fujian Province, a high-prevalence area of cryptocaryoniasis in China. The survival, diameter/number of tomonts, and infection ratio among Larimichthys crocea, Lateolabrax japonicus, Pagrus major, and Nibea albiflora were compared after artificial infection. Meanwhile, the immobilization titers of four fish species with no C. irritans infection were detected. Results showed that survival and serum immobilization titer of N. albiflora were significantly higher than those of the other three fish species. A strong negative linear correlation was found between the survival/serum immobilization titer and the mean tomont diameter. In addition, the smallest C. irritans infection ratio was found in N. albiflora, implying that the serum of fishes especially that of N. albiflora, inhibited the development of parasitic C. irritans cells, and the smallest tomont size was directly related to the number of infective theronts corresponding to the highest survival of fish. Moreover, complement activity inhibition assays suggested that the alternative complement pathway might play a major role in C. irritans resistance.

Transcriptome analysis and discovery of genes involved in immune pathways in large yellow croaker (Larimichthys crocea) under high stocking density stress.

The large yellow croaker, Larimichthys crocea, is an economically important maricultured species in southeast China. Owing to the importance of stocking densities in commercial fish production, it is crucial to establish the physiological responses and molecular mechanisms that govern adaptation to crowding in order to optimize welfare and health. In the present study, an extensive immunity-related analysis was performed at the transcriptome level in L. crocea in response to crowding stress. Over 145 million high-quality reads were generated and de novo assembled into a final set of 40,123 unigenes. Gene Ontology and genome analyses revealed that molecular function, biological process, intracellular, ion binding, and cell process were the most highly enriched pathways among genes that were differentially expressed under stress. Among all of the pathways involved, 16 pathways were related to the immune system, among which the complement and coagulation cascades pathway was the most enriched for differentially expressed immunity-related genes, followed by the chemokine signaling pathway, toll-like receptor signaling pathway, and leukocyte transendothelial migration pathway. The consistently high expression of immune-related genes in the complement and coagulation cascades pathway (from 24 to 96 h after being subjected to stress) suggested its importance in both response to stress and resistance against bacterial invasion at an early stage. These results also demonstrated that crowding can significantly induce immunological responses in fish. However, long-term exposure to stress eventually impairs the defense capability in fish.