| Summary: | The longjaw tapertail anchovy <i>Coilia nasus</i>, which migrates from ocean to freshwater for spawning in spring, is an important anadromous fish with ecological and cultural significance. To determine parasite infection in anadromous <i>C. nasus</i>, a total of 103 fish from the Yangtze River were collected and examined in 2021 and 2022. The overall infection prevalence of nematodes in <i>C. nasus</i> was 100%, with a mean intensity of 13.81 ± 16.45. The mean intensity of nematode infections in 2022 was significantly higher than that observed in 2021 across all sampling sites (<i>p</i> < 0.05). Nematodes were widely detected in the mesentery, pyloric cecum, stomach, and liver, among which the mesentery accounted for the highest proportion, reaching up to 53.52%. A total of eight ascaridoid nematodes belonging to the family Anisakidae and Raphidascarididae were identified by using morphological characters and molecular biological techniques, including two species of <i>Anisakis</i>, five species of <i>Hysterothylacium</i>, and one species of <i>Raphidascaris</i>. <i>A. pegreffii</i> was found as the predominant species, accounting for 48.65% of all identified parasitic nematodes in liver, while <i>Raphidascaris</i> sp. was the most common nematode in the mesentery, pyloric cecum, and stomach, reaching up to 39.81%, 36.21%, and 74.36%, respectively. The present study systematically investigated the parasitic status and community structure of the nematode in <i>C. nasus</i> during its migration in the Yangtze River. This research provides a foundation for studying the impact of nematode parasitism on the reproductive migration and population recruitment of <i>C. nasus</i>, and offers valuable insights for biomarker screening and nematode identification in <i>C. nasus</i>.
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