Aeromonas hydrophila is a well-known bacterial pathogen associated with mass mortalities in aquaculture. Yet, few reports are available on whiteleg shrimp-pathogenic A. hydrophila. In the present study, a virulent isolate WS05 was confirmed as a causative agent of diseased freshwater-cultured whiteleg shrimp and showed a mean lethal dose (LD50) value of 4.8 × 104 CFU mL−1. It was identified phenotypically and molecularly as an A. hydrophila strain, and exhibited susceptibility to several veterinary antibiotics extensively used in aquaculture, including cotrimoxazole, doxycycline, florfenicol, neomycin, and tetracycline. In view of the strongest inhibition zone of florfenicol against isolate WS05, the synergistic effect of the combinations of florfenicol and herb extracts was further evaluated, and the result indicated that Punica granatum extract was a potential synergist of florfenicol against isolate WS05 and the fractional inhibitory concentration index (FICI) for the florfenicol-P. granatum extract was calculated as 0.31. When combined with 7.81 mg mL−1 P. granatum extract, the minimum inhibitory concentration (MIC) of florfenicol against isolate WS05 was reduced from 0.50 to 0.03 mg L−1, and its activity against isolate WS05 was also enhanced with a significant reduction of ≥3.61 log in cell density after 24 h of treatment compared with that in the single drug treatment. In addition, the protective effect was potentiated by the combination of florfenicol and P. granatum extract, with a cumulative mortality of 36.66% (p < 0.05) and 33.33% (p < 0.05) lower than that in the single treatment with florfenicol and P. granatum extract after the challenge with isolate WS05 for seven days. As far as we know, this is the first study to describe whiteleg shrimp-pathogenic A. hydrophila and suggest P. granatum extract as a potential synergist of florfenicol against the A. hydrophila pathogen.

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Developing ecological approaches for disease control is critical for future sustainable aquaculture development. White spot syndrome (WSS), caused by white spot syndrome virus (WSSV), is the most severe disease in cultured shrimp production. Culturing specific pathogen-free (SPF) broodstock is an effective and widely used strategy for controlling WSS. However, most small-scale farmers, who predominate shrimp aquaculture in developing countries, cannot cultivate SPF shrimp, as they do not have the required infrastructure and skills. Thus, these producers are more vulnerable to WSS outbreaks than industrial farms. Here we developed a shrimp polyculture system that prevents WSS outbreaks by introducing specific fish species. The system is easy to implement and requires no special biosecurity measures. The promotion of this system in China demonstrated that it allowed small-scale farmers to improve their livelihood through shrimp cultivation by controlling WSS outbreaks and increasing the production of ponds.

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.

We report the effect of transport stress on the immune responses of the sea cucumber Apostichopus japonicus. The total coelomocytes counts, phagocytosis activity, reactive oxygen species production, acid phosphatase activity, phenoloxidase activity and catecholamine levels were measured in A. japonicus following both damp and water transportation methods. With both transport methods, stress resulted in significant elevation of catecholamine levels. Total coelomocytes counts increased following transportation, whereas phagocytic activity and reactive oxygen species production decreased. Damp transport significantly depressed acid phosphatase and phenoloxidase activity in A. japonicus. However, there were no significant differences in acid phosphatase and phenoloxidase activity after water transportation. These results show that transport stress induces modifications in the immune system of A. japonicus and that damp transport elicited more severe stress than water transport. This study increased understanding of the mechanism of transport stress inducing neuroendocrine responses and immune modification in A. japonicus. The information obtained should be helpful to optimize transport process in sea cucumber culture.