The Collaborative International Dictionary of English v.0.48:

Hausen \Hau"sen\ (h[add]"s[e^]n), n. [G.] (Zool.)
   A large sturgeon (Acipenser huso syn. Huso huso) from the
   region of the Black Sea; also called Beluga. It is
   sometimes twelve feet long, and provides the highest quality
   caviar.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Huso \Hu"so\, n. [NL., fr. G. hausen, and E. isinglass.] (Zool.)
      (a) A large European sturgeon (Huso huso or Acipenser
          huso), inhabiting the region of the Black and Caspian
          Seas. It sometimes attains a length of more than
          twelve feet, and a weight of two thousand pounds.
          Called also hausen and beluga. It is the source of
          the finest and most esteemed caviar.
      (b) The huchen, a large salmon.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Beluga \Be*lu"ga\ (b[-e]*l[=u]"g[.a]), n. [Russ. bieluga a sort
   of large sturgeon, prop. white fish, fr. bieluii white. The
   whale is now commonly called bieluka in Russian.]
   1. (Zool.) A cetacean allied to the dolphins.
      [1913 Webster]

   Note: The northern beluga (Delphinapterus catodon) is the
         white whale and white fish of the whalers. It grows
         to be from twelve to eighteen feet long.
         [1913 Webster]

   2. the sturgeon (Huso huso) native to the Black Sea and
      Caspian Sea; -- also called hausen. It is valued for its
      roe, sold as caviar, and is also used for production of
      isinglass. See also sturgeon.
      [PJC]

   3. the caviar obtained from the beluga[2]; -- also called
      beluga caviar. The caviar of the beluga is considered
      the finest sort, larger and of a taste superior to that
      obtained from other sturgeon. See also sturgeon and
      caviar.
      [PJC]