Why is raw Asian fish of higher quality .
[ of Raw fish infection.png | thumb | 300px | Differential symptoms of parasite infection by raw fish : Clonorchis sinensis ( a trematode / fluke ) , Anisakis ( a nematode / roundworm ) and Diphyllobothrium a ( cestode / tapeworm ) , all have gastrointestinal , but otherwise distinct , symptoms .