ABSTRACTTwo experiments were conducted to examine the effect of varying amounts of casein and starch relative to the amount of an α‐amylase supplement on shrimp growth and digestive processes. Amylase was supplemented to diets containing 9.5, 19.0 and 28.5% starch in a freeze‐dried nylon‐protein microcapsule form in order to circumvent potential inactivation.After a 30‐day feeding period, shrimp fed diets containing 19.0% and 28.5% starch, and supplemented with approximately 60 IU amylase/g‐dry‐diet were significantly larger (P<0.05) than diets with no amylase or a live short‐necked clam control diet. Shrimp fed 9.0% starch attained a greater mean weight than those fed 28.5% starch. These findings, evaluated collectively, indicate that a 60 IU amylase/g‐dry‐diet supplement was adequate for complete utilization of dietary starch at the 19.0% level but not at the 28.5% level.In a second study which used chromic oxide to examine the effect of an amylase supplement on the digestibility ratio of dietary starch, almost complete digestion (95.7%) was found in the group fed the α‐amylase supplemented diet containing 19.0% starch, as compared to 89.5% digestibility in the group without the amylase supplement.These studies show that up to 30% of the casein in the diet could be substituted with starch on equal weight basis without a substantial reduction in weight gain or feed efficiency, with supplementation of α‐amylase. This may allow future development of m