Zacco pachycephalus (Günther, 1868) Zacco taiwanensis Chen, 1982 Opsariichthys pachycephalus is a species of freshwater ray-finned fish belonging to the family Xenocyprididae, the East Asian minnows or sharpbellies.

It is one of the most common minnows of Taiwan, found in the entire western part of the island from sea level to 1200 m elevation.

[2] It is a small species reaching a maximum length of 16 cm (6.3 in) TL.

It is suggested that the current population structuring reflects colonization from two glacial refugia, formed when the cooler climate during the last glacial period restricted this species to lower elevations: one on the land bridge that connected Taiwan to the Asian mainland, and the other one in the south, east of the Gaoping River.

[2] Opsariichthys pachycephalus show two peak spawning periods, one in spring (February–April) and the other one in summer (June–August), the former being the main one.