This study was designed to evaluate the effect of replacement of fish meal with a marine microalgae species spirulina (Spirulina platensis) on Pacific white shrimp Litopenaeus vannamei post larvae for 90 days. Spirulina was used with four levels (5, 10, 15 and 20). Experiment was carried out in 15 tanks with water volume 150 L. Each treatment had 3 replicates, each tank contained 50 Post-larvae of 0.02 g body weight. Shrimp were fed the experimental diets containing about 40% protein twice daily at 14% from body weight (initial weight) and readjusted gradually to 5% at the end of the experiment. Growth performance of shrimp was recorded biweekly. It was found that the best treatment of growth performance, feed utilization and economic evaluation under these experimental conditions was the treatment in which fish meal was replaced by 10% spirulina