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Enteritis is known as a major disease in snakehead fish Ophiocephalus argus aquaculture and has resulted in large economic losses. Yet only scarce information is available on Aeromonas veronii as a causal agent for enteritis in O. argus. In this study, a virulent strain, temporarily named HY2, was isolated from diseased snakehead fish suffering from enteritis, and was identified as A. veronii through molecular and phenotypic methods. In addition, the HY2 isolate showed an LD50 value of 2.8×10 5 CFU mL-1 , and was highly sensitive to aminoglycosides, macrolides, polypeptides, quinolones, sulfonamides and tetracyclines antibiotics. To the best of our knowledge, this is the first report of A. veronii as a potential pathogen of enteritis in snakehead fish.

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The particle swarm optimization(PSO) algorithm has exhibited good performance on continuous optimization problems in static environment. However, there are lots of real-world optimization problems that are dynamic and discrete, which is a new research field of PSO. So a dynamic discrete PSO(DDPSO) algorithm is proposed in this paper. In this algorithm, we design a new strategy of environmental monitoring and response. When environment is changed, it can be apperceived by the change of fitness and position of particles and be responded by environment sensitivity and environmental change gene in time. Finally, to analyze the convergence of DDPSO based on the solving of zero state response in discrete-time systems, we get its convergence condition and motion track of particles. As a result, we find that DDPSO has good convergence and diversity of swarm owing to environmental change gene which has randomicity and variability.