Mergus is the genus of the typical mergansers fish-eating ducks in the subfamily Anatinae. 

1/ Scaly-sided merganser or Chinese merganser (Vịt mỏ nhọn, Mergus squamatus)
2/ Red-breasted merganser (Vịt cát ngực đỏ, Mergus serrator) 

anas, anatis: Latin duck.
The genus name Mergus is a Latin word to refer to an unspecified waterbird.
Mergus is a Latin word meaning "diver" or "waterfowl," derived from the verb mergere, which means "to dip" or "plunge". It was used by ancient authors to refer to an unspecified diving seabird.