PURPOSE: To provide an inexpensive method for treating Phaffia rhodozyma.

CONSTITUTION: The availability of astaxanthin from cells of Phaffia rhodozyma is improved by reacting the cells with sulfuric acid, hydrochloric acid or a mixture thereof and heating the obtained slurry at 60-90°C. Typically the heating is effected for 2 to 4 hours, preferably at about 80°C. The acid used is preferably of a concentration of about 0.75 N to 1 N. One use of the treated cells is in aquaculture where astaxanthin is used as a dietary supplement in the farming of fish and crustaceans.