PROBLEM TO BE SOLVED: To complement the normal growth of a floating larva from a hatching period to a bottom landing period for a bivalve floating larva with a risk causing a production failure, and an Atrina floating larva with few possibility of production, and reduce mass mortality and growth stagnation so as to achieve improvement of seedling production number.SOLUTION: A feed for a bivalve floating larva is provided in which a water soluble functional component is embedded in a hardly water-soluble protein. The water soluble functional component is taurine, or the hardly water-soluble protein is zein. Or, the water soluble functional component is taurine and the hardly water-soluble protein is zein.