This study aimed to elucidate the parasitic nematode infecting the bile ducts of striped catfish. A total of 1570 fish specimens, weighing between 400.5 and 899.1 g each, were examined. A parasitological analysis revealed that 607 fish samples were infected with nematodes, with typical clinical signs including swollen in both the common bile duct and gallbladder, several white cysts in the common bile ducts, and gallbladders exhibiting a dark green coloration. Examination of the common bile ducts in striped catfish revealed the presence of two distinct parasitic nematode morphotypes. Free-living nematodes were observed residing within the lumen, the central cavity, of the common bile duct. Additionally, larval nematodes were encapsulated within cysts lining the duct wall, suggesting a more chronic parasitic association. The infection rate of worms in the common bile duct was prevalent from November to April, with the most significant infection rate occurring in March (67.1%). The intensity of free-living nematode infection was the peak in March, with a mean of 6.7 ± 1.5 worm/gallbladder, and the peak level of larval nematode encapsulation was in November, with 9.4 ± 3.8 encysted larvae/common bile duct. The highest cumulative fish mortality rate was observed in February (2.1 ± 0.4%). Morphological analysis revealed the roundworms to be white and elongated with a slight narrowing at the mid-esophageal region. The mouth extended posteriorly towards the abdomen, and a well-developed, funnel-shaped esophagus was observed. Further analysis using 18S rRNA gene sequencing confirmed the identity of the parasite within the common bile duct of striped catfish as Cucullanus bourdini.