The effects of CuSO4 on Cryptocaryon irritans tomonts and its potential mechanism

Abstract

Cryptocaryon irritans infection could cause huge economic losses to the marine fish industry. Due to the lack of targeted anti-parasitic drugs, CuSO4 is widely used in the prevention and control of parasitic diseases in aquaculture. C. irritans tomonts are “cyst like, reproductive stage” of the parasites life cycle that is highly resistant to different compounds and drugs. In this study, we explored the effects of CuSO4 on the C. irritans tomonts, incubation rate, morphological difference and transcriptome changes. The results showed that the tomonts treated with CuSO4 had a thicker cyst wall than the control group. Ultrastructural analysis of C. irritans tomonts exhibited less encapsulated content after CuSO4 treatment, while tomonts organelle was abundant in the control group. The hatching rate of tomonts treated with CuSO4 (10 mg/L) was lower (25.92–40.73%) than that of tomonts without treatment with chemical drugs (80.77–95.45%). Differentially expressed genes (DEGs) analysis revealed that 223 DEGs including 160 DEGs up-regulated and 63 DEGs down-regulated genes were identified. In GO analysis, relatively more upregulated DEGs were annotated into growth, reproduction and reproductive process, while down-regulated DEGs were mainly annotated into biological adhesion, immune system process, and supramolecular complex. In the KEGG enrichment analysis, Taste transduction (ko04742), Circadian entrainment (ko04713), Vascular smooth muscle contraction (ko04270) and Platelet activation (ko04611) were the top 4 pathways with the highest degree of enrichment. In addition, IP3R, AC, PKG, MLCP and MPase genes involved in regulating calcium flow play an important role in these pathways. Taken together, our results indicate that CuSO4 may affect the C. irritans tomonts by influencing the calcium flow.