Survey for the presence of ascaridoid larvae in the cinnamon flounder Pseudorhombus cinnamoneus (Temminck & Schlegel) (Pleuronectiformes: Paralichthyidae).

The cinnamon flounder Pseudorhombus cinnamoneus is a frequently consumed marine fish in China. However, the occurrence of ascaridoid larvae in P. cinnamoneus remains unclear. In the present study, a total of 85 P. cinnamoneus caught from the Yellow Sea (off Shidao, 36°52'57″N, 122°26'42″E) in 2011, which is located between mainland China and the Korean Peninsula, was investigated for ascaridoid larval infection. Four ascaridoid larval types, including Anisakis type I of Berland (1961), Hysterothylacium type of Smith (1983), Hysterothylacium type HL of Guo et al. (2014) and Raphidascaris type of Zhao et al. (2016), were detected in this important food fish. These larval types were identified as Anisakis pegreffii, Hysterothylacium aduncum, H. sinense and Raphidascaris lophii, respectively, using PCR-based restriction fragment length polymorphism (PCR-RFLP) analysis and sequencing of the ITS region of nuclear ribosomal DNA (rDNA). The third-stage larvae of H. sinense are reported from Chinese waters for the first time. The prevalence of H. sinense was 100% and represents the predominant species of the ascaridoid larvae found in P. cinnamoneus. The prevalences of A. pegreffii and H. aduncum were 44.7% and 81.2%, respectively. Phylogenetic analyses based on ITS sequences were performed to elucidate the genetic relationships of these ascaridoid nematodes. The present study increases the knowledge and distribution of ascaridoid larvae in this area of Yellow Sea. The high prevalence of ascaridoid larvae in P. cinnamoneus shows that an assessment needs to be undertaken to assess the risk these parasites may pose to public health.