The goal of this study was to characterize the nutritional contribution of microalgae to white-legged shrimp and optimize fish meal (FM) and fish oil (FO) inclusion levels in their diets in the presence of microalgae. Phytoplankton composition was first determined in a typical Peruvian intensive commercial shrimp farm and in a semi-closed greenhouse-covered reservoir. A predominance of 76.3% cyanobacteria was observed for most of 9 months in all shrimp ponds. However, with the fertilization program in a reservoir tank, 60.7% diatoms and 22.8% cyanobacteria predominated. Thus, with the imposed fertilization regimen, the microalgae composition was manipulated to be different than that in commercial shrimp ponds. The microalgae composition was then evaluated along with different dietary levels of FM and squid meal (SM) in a feeding trial to evaluate the potential of phytoplankton to reduce FM and SM levels in shrimp feeds. Six diets were formulated to contain either 5, 10 or 20% SM combined with either 6.5 or 12% FM. Dietary effects on growth and survival were compared in a "clear-water system" (CWS) and a "green-water system" (GWS). Results suggest that 6.5% FM and 5% SM can be used as a cost-effective combination in feeds for shrimp. The effects of different dietary levels of FO and soybean lecithin (LT) on shrimp growth in CWS and GWS were evaluated in another feeding trial to determine if dietary phospholipids and phytoplankton increase the availability of essential fatty acids (EFAs) to shrimp. Six diets were formulated to contain 1, 2 or 3% FO combined with either 1 or 4% LT. Shrimp fed diets containing 1% LT and 1% FO in both systems had significantly lower weight gain and higher feed conversion ratio. Cephalothorax lipids and phospholipids were higher in shrimp fed diets containing 4% LT. Inclusion of 4% LT increased the availability of EFAs, and could contribute to reduce the FO in shrimp diets. The contribution of phytoplankton to shrimp weight gain, varied from 38.8 to 60.6%. This study demonstrated that cost-effective diets could be formulated with reduced inclusion levels of FM and FO considering the contribution of microalgae to the nutrition of shrimp.