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The gut microbiota composition of sea cucumber (Apostichopus japonicas) was investigated using high-throughput sequencing techniques. The mRNA expression of complement component 3 and lysozyme genes was evaluated using quantitative fluorescence PCR. Sea cucumbers were fed with a basal diet (control group) and an experimental diet supplemented with Codonopsis pilosula (experimental group) for 30 days. The results showed that the alpha diversity of the gut microbiota was changed in different indices, including Chao1, the abundance-based coverage estimator, the Shannon index, and Good’s coverage. Dietary C. pilosula promoted the proliferation of the Flavobacteriaceae family of the Proteobacteria phylum and reduced the relative abundance of the Verrucomicrobiaceae family of the Verrucomicrobia phylum. We concluded that dietary C. pilosula supplementation could alter the network interactions among different microbial functional groups by changing the ecological network’s microbial community composition and biological evolution. A positive effect on A. japonicus immune responses in the gut was seen via increasing the mRNA expression of the complement component 3 and lysozyme genes. It seems to happen via modulating the balance in gut microbiota.

Bacteriosis is a major economic problem affecting the farming industry of whiteleg shrimp Penaeus vannamei. Little information is available on Providencia rettgeri as a possible pathogen for P. vannamei. In this study, a virulent strain, here named S6, was isolated from diseased P. vannamei, identified phenotypically, and molecularly, as P. rettgeri. A phylogenetic tree was constructed to examine the taxonomic position and relatedness of isolate S6 to other P. rettgeri isolates. When screened against a range of common veterinary antibiotics, isolate S6 exhibited resistance to aminoglycosides and sulfonamides antibiotics in aquaculture. To the best of our knowledge, this is the first report of P. rettgeri as a causal agent of bacteriosis in freshwater farmed P. vannamei.

Tail rot disease is the cause of significant economic damage in freshwater farmed Murray cod Maccullochella peelii. Only scarce information is available on Aeromonas hydrophila as a possible causal agent for this disease. In this study, a virulent strain, temporarily named XY3, was isolated from diseased codfish suffering from tail rot disease, and identified as A. hydrophila through phylogenetic analysis and phenotypic characteristics. A. hydrophila possesses multiple virulence genes including aerA, ahpA, alt, ast and hlyA genes. In addition, it appears that isolate XY3 has developed multiple resistances to cephalosporin, chloromycetin, glycopeptides, macrolides, nitrofuran, and penicillin drugs, as well as to aminoglycosides, sulfonamides, and tetracyclines antibiotics for veterinary uses in aquaculture as revealed when screened against a range of common antibiotics. To the best of our knowledge, this is the first report of tail rot disease caused by A. hydrophila in freshwater farmed codfish.