Abstract: The present paper deals with the infection of the metacercarial cysts of Centrocestus formosanus on the gill filaments and gill rakers of Aristchthys nobilis from August 1993 to November 1994. The results indicated that the prevalence of the gill filaments and gill rakers ranged from 0 to 100%. The mean infections intensity of the gill filaments and gill raters varied from 0 to 109.15 and 0 to 125.57, respectively. The relative density or abundance of the metacercarial cysts on the gill filaments and gill rakers was 0 to 97.76 and 0 to 125. 57 respectively. The preavlence, mean intensity and the relative density of the metacercarial cysts on the gill filaments and gill rakers increased with the growth of the host Aristchthys nobilis when the body length was less than 90 mm, declined when the body length of the host exceeded 90 mm, which on the gill rakers changed obviously. No metacercarial cysts occurred on the gill rakers when the body length of the host exceeded 141.7mm. The metacercarial cysts percentage of the gill filaments increased from 0 to 100% with the growth of the host, but those of the gill rakers declined from 100% to 0 with the growth of the host.