To assess the effects of abiotic factors on Argulus japonicus occurrence in freshwater ecosystem, we sampled fish, free-swimming parasites, and submerged objects from rivers, fish farms, and ponds (reservoirs and lakes) at 27 locations in Guangdong province, China, from July, 2010, to March, 2013. Friedman's test and Spearman's correlation coefficient (r) were used to investigate relationship between A. japonicus occurrence and abiotic factors in three aquatic systems. Correlation of monthly density, mean density, prevalence, abundance, and intensity of A. japonicus with water temperature, biochemical oxygen demand of 5?days, chemical oxygen demand, and ammonia were very significant, but negative relation with pH, dissolved oxygen, and total phosphorus components. Nevertheless, total nitrogen components showed an insignificant impact on A. japonicus incidence. In addition, water temperature and stability were two key factors controlling A. japonicus infestation. Our study revealed the capability of A. japonicus to inhabit and prevail in heavily polluted freshwater. Results demonstrate that A. japonicus has good adaptability to the environmental factors' stress but cannot be used as a biological indicator of environmental pollution.
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