A fish feed additive is used which contains beta -carotene containing Dunaliella algae powder stabilized against oxidation and migration into the water. The fish feed is prepared by mixing 100 parts by weight of a Dunaliella algae powder with 15-50 parts by weight of a cyclodextrin while stirring. The final fish feed is obtained by blending 10 parts by weight of this additive with 200-500 parts by weight of a common fish feed. The fish feed additive is in the form of dry fine granules. The fish feed additive effectively promotes growth and delivers beta -carotene to the fish.
