Search

Red abdominal shell disease is a major disease that has caused significant economic losses in Chinese soft-shelled turtle Pelodiscus sinensis aquaculture. Yet scarce information is available on Aeromonas dhakensis as a causal agent of red abdominal shell disease in P. sinensis. In the present study, a haemolytic and proteolytic A. dhakensis isolate (F04) was demonstrated as a causative agent of red abdominal shell disease in cultured P. sinensis. It carried virulent aerolysin, heat-labile cytotoxic enterotoxin, polar flagella, and lipase-encoding genes aer, alt, flaA, and lip, exhibited the mean lethal dose (LD50) value of 4.27×105 CFU/ml in P. sinensis, and developed multiple resistances against aminoglycosides, chloramphenicols, cephalosporins, lincosamides, macrolides, penicillins, peptides, sulfonamides, and tetracyclines antimicrobials. To our knowledge, this is the first study to identify a multiply resistant A. dhakensis strain as a pathogen of red abdominal shell disease in P. sinensis, and the findings of this study can also provide valuable insights into the virulence and antimicrobial resistance in Chinese soft-shelled turtle-pathogenic A. dhakensis.

The development of microbial communities is important for the growth of the fat greenling Hexagrammos otakii; however, the relationship between microbial communities and fish diet is poorly understood. Here, we used metagenomics sequencing to investigate the gut microbiota of H. otakii at three key time points during development. The gut microbial diversity and community composition of H. otakii presented stage-specific signatures and appeared to shift with different diets and environmental conditions such as NH4 + -NO2- etc. Metagenomics analysis indicated that the dominant phyla were Proteobacteria and Firmicutes. With dietary changes from rotifers and Artemia to formulated feed, the dominant genera shifted from Vibrio and Photobacterium to Lactococcus, and variations in the gut microbiota increased with age. Based on metagenomics functional annotation using the Kyoto Encyclopedia of Genes and Genomes database, growth and diet at different stages affected the metabolic function of the gut microbiome by activating carbohydrate and amino acid metabolism while weakening lipid and nucleotide metabolism. In addition, as predicted by the Carbohydrate-Active enZymes database, glycoside hydrolase and glycosyl transferases may be involved in food degradation. Our results suggest that the H. otakii gut microbiota assembly was coupled to animal development and host age-associated biotic features and changes. Diet had a considerable effect on these distinct communities at different times, indicating that the fish gut microbiota rapidly adapted to dietary shifts. The microbiota therefore likely plays an indispensable role in nutrient turnover and fermentation. These findings can provide guidance for the development of probiotics and the application of feed additives.

Wang et al. develop a shrimp polyculture system that prevents white spot syndrome outbreaks by introducing specific fish species. The system is easy to implement and requires no special biosecurity measures which makes it ideal for small-scale farmers.

Vibrio ponticus is a vital pathogen with potential danger for aquaculture animals. Yet V. ponticus pathogenic to the coral trout Plectropomus leopardus is still unknown. In this study, a virulent bacterial strain, temporarily named DX2, was isolated from diseased coral trout suffering liver necrosis with cell vacuolar degeneration, and was identified molecularly and phenotypically as V. ponticus. Besides, the DX2 isolate showed an LD50 value of 6.64×105 CFU mL-1, developed multiple resistances to cephalosporins, macrolides, penicillins, peptides, and sulfonamides antimicrobials, and was highly susceptible to doxycycline and florfenicol in aquaculture use. To the best of our knowledge, this is the first report of the pathogenicity of V. ponticus to the coral trout, and the findings provide a reference for the control of pathogenic V. ponticus in the coral trout.

In this study we sequenced the genomes of three economically important swimming crabs Portunus trituberculatus, Charybdis japonica, and Callinectes sapidus using the next-generation sequencing approach and made a basic assembly. The genomes of the three species are characterized with high heterozygosity (>1.2%) and high repeat content (>50%). Genome comparative analysis revealed 40 long conserved fragments (>5,000 bp) among the three species, most of them are involved in cardiac-related biological process. Relative higher genome similarity was found between P. trituberculatus and C. japonica that are belong to different subfamilies, compared to that between P. trituberculatus and C. sapidus which are from the same subfamily. It is inconsistent with their phylogenetic evolutionary trees inferred from previous mitochondrial DNA coding fragments and a conserved ANK2 protein fragment from this study. We speculated that the high genome similarity between P. trituberculatus and C. japonica might be attributed to their same inhabit range in which the genome is subject to the same environment selection, and the inconsistence between genome similarity and phylogenetic relationship is caused by the different evolutionary rates of coding DNA and non-coding DNA under environment selection.

The hemorrhagic disease has become a major bottleneck in yellow catfish Pelteobagrus fulvidraco aquaculture. Yet scarce information is available on Bacillus subtilis as a pathogen of hemorrhagic disease in cultured yellow catfish. In this study, a virulent isolate, temporarily named HS5, was isolated from hemorrhagic disease-infected cultured yellow catfish, and was identified phenotypically and molecularly as B. subtilis. In addition, isolate HS5 showed an LD50 value of 5.20×106 CFU/ml in yellow catfish, exhibited beta-haemolytic activity, harbored the virulent entFM gene, and displayed high susceptibility to enrofloxacin and florfenicol in aquaculture use. To the best of our knowledge, this is the first report of B. subtilis as a pathogen of hemorrhagic disease in farmed yellow catfish. [ABSTRACT FROM AUTHOR]