In order to elucidate the relationship between "Cryptocaryoniasis" caused by Cryptocaryon irritans infection and secondary bacterial infections in Trachinotus ovatus, in the report, the continuous sampling of the naturally infected fish in offshore deep-sea cage farming systems and the laboratory-reared individuals were conducted, the artificial infection experiments with Cryptocaryon irritans were in order to elucidate the relationship between "Cryptocaryoniasis" caused by Cryptocaryon irritans infection and secondary bacterial infections in Trachinotus ovatus, in the report, the continuous sampling of the naturally infected fish in offshore deep-sea cage farming systems and the laboratory-reared individuals were conducted, the artificial infection experiments with Cryptocaryon irritans were performed, and the correlations between the infection intensity of the parasite, secondary bacterial infection rates, and the hepatic bacterial loads were investigated, and the dominant bacteria in the livers of diseased fish was identified. The results demonstrated that the secondary bacterial infection rates and the hepatic bacterial loads significantly increased with the increase of the severity of Cryptocaryon irritans infection; the peak values of the secondary bacterial infection rates and the hepatic bacterial loads were observed at 168 h post-infection; among 93 dominant bacterial strains isolated from the liver tissues of the farmed Trachinotus ovatus in the natural marine environment, Photobacterium damselae and Vibrio harveyi were identified as the predominant pathogens. This study provides a theoretical basis for the prevention and treatment of Cryptocaryon irritans infection and its associated secondary bacterial infections.

In order to investigate the effects of formaldehyde disinfection on the symbiotic bacterial community on the surface of the tilapia eggs during artificial incubation, in the report, 16S rRNA high-throughput sequencing technology was used to analyze and predict the surface symbiotic bacterial community of the unsterilized tilapia eggs (pre disinfection eggs, EP) collected from tilapia parent fish pond and the eggs (post disinfection eggs, E2) placed in the incubation system on the second day after formaldehyde disinfection. The results indicated that during spring, autumn, and winter, the number of OTUs in EP fish eggs were higher than that in E2 fish eggs, and the Ace and Chao1 indices of EP fish eggs were significantly higher than those of E2 fish eggs (P<0.05), the Simpson index of EP fish eggs were significantly lower than that of E2 fish eggs (P<0.05). The PcoA analysis results indicated that before and after disinfection, there were significant differences between the microbial community structure in all four seasons (P<0.05). At the phylum level, compared to EP fish eggs, the abundance of Bacteroidetes on E2 fish eggs increased, and which was more significant in autumn (P<0.05). At the genus level, the abundance of Cetobacterium, Bacillus, and Vibrio genera on E2 fish eggs were significantly lower than that on EP fish eggs (P<0.05), while the abundance of Flavobacterium, Pseudomonas, and Chryseobacterium significantly increased (P<0.05). The prediction of microbial community functions showed that amino acid transport and metabolism, inorganic ion transport and metabolism, and carbohydrate transport, and metabolism were the main predictive functions. After being disinfected with formaldehyde and transferred to an indoor incubation system for 2 days, the surface symbiotic bacterial community structure of tilapia eggs underwent significant changes and the species diversity significantly decreased. The abundance of potential probiotics decreased. There were no significant differences in the microbial functional characteristics. Our finding provided the theory guidance and the basis for disease prevention and control in the artificial hatching system of tilapia eggs.