Yanhua Zhao

Grass carp in aquaculture exhibited symptoms of bacterial infection leading to mortality. To investigate the cause of the disease and control grass carp infections, samples from diseased grass carp were collected, and a bacterial strain named XH-1 was isolated from the internal organs of the infected fish. Artificial infection experiments were conducted to determine whether the isolated strain XH-1 was the pathogenic bacterium. The biological characteristics of the isolated strain were studied through a 16S rRNA sequence analysis, physiological and biochemical identification, and phylogenetic tree construction. Extracts from 14 traditional Chinese herbs were tested to evaluate their bacteriostatic and bactericidal effects on the isolated strain. The regression infection experiment confirmed that the isolated strain XH-1 was the pathogenic bacterium causing the grass carp disease. Biological characterization studies identified the bacterium as Aeromonas veronii, which is clustered with A. veronii MW116767.1 on the phylogenetic tree. Among the 14 Chinese herbal extracts, Lignum sappa, Pericarpium granna, Artemisia argyi, Scutellaria baicalensis Georgi, Coptis chinensis, and Artemisiacapillaris thunb exhibited significant bacteriostatic effects on XH-1. Lignum sappa showed the highest sensitivity to A. veronii, with the largest inhibition zone diameter, and its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were 7.813 mg/mL and 15.625 mg/mL, respectively. As the concentration of Lignum sappa extract increased, its bacteriostatic and bactericidal effects strengthened. When the concentration exceeded 14 mg/mL, it maintained strong bactericidal activity over 32 h. This study on A. veronii XH-1 provides theoretical insights for the prevention of grass carp aquaculture diseases and the use of traditional Chinese herbs for treatment.

Chitin synthase is an essential enzyme of the chitin synthesis pathway during molting. In this study, we identified and characterized a chitin synthase (EsCHS) gene in the Chinese mitten crab, Eriocheir sinensis. The spatio-temporal expression and functional role of EsCHS were investigated. The open reading frame of EsCHS was 4725 bp long and encoded 1574 amino acid residues that contained the typical domain structure of the glycosyltransferase family 2. Phylogenetic analysis revealed that EsCHS belongs to the group I chitin synthase family. The expression of EsCHS was found in regenerative limbs, the cuticle and the intestines. During the molting cycle, EsCHS began to increase in the pre-molt stage and reached a significant peak in the post-molt stage. The knockdown of EsCHS resulted in the significant downregulation of chitin biosynthesis pathway genes, including TRE, HK, G6PI, PAGM and UAP. Moreover, the long-term RNAi of EsCHS resulted in thinning procuticles, abnormal molting and high mortality, suggesting that EsCHS is indispensable for the formation of chitin in the cuticle during molting. In conclusion, EsCHS is involved in the chitin biosynthesis pathway and plays an important role in molting in E. sinensis. These findings highlight the potential of incorporating EsCHS into selective breeding programs to optimize molting regulation and improve growth performance in crustacean aquaculture.

Aeromonas hydrophila is one of the most important pathogenic bacteria for aquaculture animals, such as fish and crustaceans. In this study, we isolated a pathogenic bacterial strain, named Y-SC01, from dark sleeper ( Odontobutis potamophila ) with rotten gills; the strain was identified as A. hydrophila by physiological and biochemical tests.