The present work aimed at studying the effect of drying temperature on the biochemical contents of Spirulina platensis to choose the best temperature that can be used for drying without affecting its contents to be used as a fish diet, with a good quality, low price and to give the immunity to fish in fish farms. Open air and temperatures (60^oC and 120^oC) were applied for drying Spirulina platensis. The alga was cultivated on large scale in concrete ponds (25 and 50 m³) to be used as fish meal. The crude protein content of the dried matter in S. platensis biomass was 59.1, 63.2, and 64.8% in case of open air, 60^oC and 120^oC respectively. Also there are no significant differences measured of amino acids content on open air, 60 ^oC and 120 ^oC. The nutritional value of protein is due to its amino acids contents which were of 49 %, 49% and 50% for the dried matter at open air and 60^oC and 120^oC respectively. Also, the lipid contents, carbohydrates, fibers and ash were 0.74%, 20.78%, 0.18% and 8.8% respectively in open air, 0.78%, 18.9%, 0.22% and 8.8% at 60^oC and 0.94%, 19.74%, 0.12% and 9.0% respectively at 120 ^oC. The results revealed that the concentrations of chemical contents (lipid, carbohydrates, fibers and ash) were higher at 120 ^oC than those at the other two procedures. The concentrations of crude protein (64.8 %) and amino acids (50%) were also higher at 120 ^oC. It was found that there is no difference between the three procedures of drying but drying at 120 ^oC saves time and therefore it is better to be used. Sixteen weeks of feeding was conducted to investigate the effect of fish meal replacement with Spirulina on growth performance and body weight. About 20% increase of weight gain and with highly significant average daily gain 0.450 and 0.546 for diet1 (control) and diet 2 (Spirulina diet) respectively and feed conversion ratio were 1.189 and 1.333 for diet1 (control) and diet 2 (Spirulina diet).  The use of the harvested alga S. platensis was to solve the problem of availability as protein source not only as fish feed but also saving aquatic environment.