What is a half cow half fish called?

A half cow, half fish creature is often referred to as a "mermaid" in folklore, though traditionally mermaids are depicted as half woman, half fish. There isn't a specific term for a creature that is literally half cow and half fish, as such a hybrid does not exist in mythology or Biology. In creative contexts, it could simply be described as a "cowfish" or a "fisher" for fun, but these are not established terms.