Abstract: Objective To investigate Hysterothylacium aduncum （Anisakidae） infection in marine fishes from Bohai Sea and Yellow Sea. Methods Nematodes were collected from the digestive tract of fishes， fixed with hot 4% formalin and preserved in 70% ethanol for study. The specimens were cleared in lactophenol for light microscopical examination， and properly treated for scanning electron microscopy （SEM）. Results Among the fishes examined， 14 out of 93 species （15.1%） were found infected by H.aduncum， with a higher prevalence in the fish of Lophius litulon（66.7%）， Scomber-omorus niphonius（47.5%）， and Gadus macrocephalus（33.3%）. H.aduncum infection was first recorded in elasmobranch-Raja smirnovi. Morphological differences of H.aduncum were observed， including the width of lateral alae and the length of intestinal caecum. Conclusion H.aduncum in fishes of Bohai Sea and Yellow Sea in China may be a complex species， and its high prevalence in some fishes reminds the risk of anisakiasis by eating raw fishes.

Key words: Anisakidae, Hysterothylacium aduncum, Scanning electron microscopy, Anisakiasis