PURPOSE: To obtain an artificial formula feed of a stable quality capable of remarkably promoting the growth of snails by using a D-mannuronic acid-rich type alginic acid as alginic acid.

CONSTITUTION: This feed is obtained by blending a D-mannuronic acid-rich type alginic acid as alginic acid therein. The feed is obtained by mixing, e.g. the D-mannuronic acid-rich type alginic acid with other feed raw materials, then hydrating and pasting the resultant mixture, forming the prepared paste into the shape of pellets, subsequently immersing the pellets in a solution such as a calcium chloride solution and gelatinizing the alginic acid. The amount of the added D-mannuronic acid-rich type alginic acid is preferably 10-50wt.%. Furthermore, the feed can be applied to snails which are objects of culture, e.g. Haliotis discus hannai Ino, Notohaliotis discus Reeve or Turbo cornutus Solander.