Microalgae have been capably used as additive to boost the fish performance and welfare because of their unique nutritional properties and functional bioactive compounds. Thus, factorial experimental design (4 × 2) investigated the effect of dietary dried Golenkinia. longispicula (0.0, 5, 10 and 15 g kg−1 diets) supplementation used in Nile tilapia, Oreochromis niloticus on growth, feed efficiency, hematological, biochemical parameters, antioxidant activity, immunity, and associated gene expression reared under two stoking densities 100 fish m3 (SD100) and 200 fish m3 (SD200). Fingerlings (initial weight of 3.29 ± 0.16 g) were randomly assigned into twenty-four fiberglass tanks (0.5 m3; 250 L volume of water) in triplicate for each treatment at two stocking density SD100 and SD200 for 90-days. Three times per day at 9:00 a.m., 11:00 a.m., and 2:00 p.m., four isonitrogenous (32.89 g kg−1 CP) and isocaloric (17.86 …