Cyclospora cayetanensis was identified as the cause of large outbreaks of diarrhea in many parts of the world, but its host range and reservoirs remains poorly defined. Recently, oocysts resembling the C. cayetanensis were detected in dairy cattle fecal specimens from China. The 18S rDNA from two of these Cyclospora-like oocyst specimens from dairy cattle was amplified and sequenced. Phylogenetic analysis indicated that these cattle-associated Cyclospora-like organisms are nearly identical to each other and belong to the group of primate-derived Cyclospora, which are the closest known relatives of C. cayetanensis; while these cyclosporans constitute a coherent clade within the diverse group of Eimeria species. Moreover, on the basis of our finding that ruminant- and avian-associated Eimeria species are different in MnlI sites, a new PCR-restriction fragment length polymorphism protocol with primers NesCycF and NesCycR was developed to distinguish the Cyclospora species from ruminant-associated Eimeria species.

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.

Argulus japonicus Thiele, 1900 was originally described from China, but has spread to Europe, Africa, Australia, and North America. An ultrastructural description of A. japanicus has been done as one of the most common fish ectoparasites which has a high affect on fish life. The description was based on light and scanning electron microscopes studies using 13 females and 7 males which were collected from Shunde city in Guangdong Province, China. Typical Argulus body and body's appendages are associated with our specimens, carapace covers fourth leg, and scales separate uniformly on frontal and lateral lobes, ventral surface of thorax is ornamented by scales contrary of the dorsal surface which is quite smooth, various shapes of scales have been detected on second maxillae. Location and structure of copulatory accessory, number and structure of overlapping sclerites of sucking disk rim, melanophores patches of male, second swimming leg structure, and parasite's total size are the most important criteria which may be used to distinguish between male and female. Moreover, new classification criteria of Argulide, obtained by scanning electron microscopic study of previous species, are discussed.

This study investigated the genetic variability within fish louse Argulus japonicus (Crustacea: Branchiura) from Africa, Middle East, and Asia by polymerase chain reaction in three mitochondrial DNA (mtDNA) regions, namely, cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunits 1 and 4 (nad1 and nad4). Six different sequences from a portion of the cox1 gene (pcox1) and a portion of the nad1 and nad4 genes (pnad1 and pnad4) for ten adult specimens from infected fish in China, Egypt, and Syria were amplified separately from individual and the amplicons were subjected to direct sequencing. A + T percentages were 68.8-69% for pcox1, 77.1-77.6% for pnad1, and 60.4-60.9% for pnad4. Among all the collected parasites, A. japonicus sequence variations were 0.0-1.9% for cox1, 0.0-2.3% for nad1, and 0.0-0.8% for nad4. In rivers, sequence variations among all individuals were 0.4-0.8% for cox1, 1.0-2.3% for nad1, and 0.4-0.8% for nad4, while sequence variations among all the collected parasites in fish farms were 0.6-1.9% for cox1, 0.0-1.7% for nad1, and 0.2-0.6% for nad4. The nad1 was the most variable gene among selected markers, while nad4 was a more conserved gene than cox1. All isolates of A. japonicus were sister to Argulus americanus in phylogenetic tree and they grouped together in one sub-clade, while isolates from China and Egypt fish farms were closely clustered together. However, moderate genetic drift and slight mutation could be observed among A. japonicus individuals. These findings demonstrated the convenience and attributes of the three selected mtDNA sequences for population genetic studies of A. japonicus where nad1 is a new and reliable marker to detect the sequence variation among A. japonicus individuals.

This study aimed to demonstrate the ability of Argulus japonicus to infect a wide range of freshwater fishes, as well as to understand the effects of fish origin and host body size on the incidence of A. japonicus. Samples of cultured and wild fish were collected randomly from July 2010 to March 2013, using angling, long-lining, gill-netting, and trapping from rivers and fish farms in Guangdong province, South China. Eight fish species were found to be heavily infected including the common carp, the goldfish, the black carp, the silver carp, the brown trout, the rainbow trout, the mandarin fish, and the perch. Furthermore, the black carp, the brown trout, and the mandarin fish were recorded as new hosts for the first time. During the present study, a total of 2,271 fishes were examined, out of which 712 fishes were found to be infected by a total of 1,443 A. japonicus. Abundance and intensity of A. japonicus infection were significantly influenced by origin of fishes (cultured and wild) and total length (class I, <250 mm; class II, 250-350 mm; and class III, >350 mm) of fish species, whereas varied impacts on prevalence of infection were observed. The correlation between total length of fishes and prevalence of A. japonicus infection was variable, where no significant correlation was observed in the black carp, the silver carp, the mandarin fish, and the perch. In spite of the weak negative correlation between body size of the silver carp and prevalence of infection, A. japonicus was the most abundant and intensive in the silver carp. Thus, aquaculturists should pay particular attention to the control of these fish lice due to its host biodiversity.