The Collaborative International Dictionary of English v.0.48:

Zaerthe \Zaer"the\, n. (Zool.)
   Same as Z[aum]rthe.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Zaumrthe \Z[aum]r"the\, n. (Zool.)
   A European bream (Abramis vimba). [Written also zaerthe.]
   [1913 Webster]