This study examines the effects of stocking density on the growth performance of juvenile Nile tilapia (Oreochromis niloticus) and spearmint (Mentha spicata) in a recirculating aquaponic system over a 120-day production cycle. Three stocking densities were tested: 40 fish/m³ (Group G1), 80 fish/m³ (Group G2), and 120 fish/m³ (Group G3). The experiment was conducted at the National Agricultural Research Center (NARC) in Palestine, using 1000-liter units equipped with biofiltration systems and standardized environmental controls. Fish were fed a diet containing 35% crude protein, while mint plants (10 plants per unit) were cultivated simultaneously without additional nutrient supplementation. Data were analyzed using one-way ANOVA followed by Tukey’s HSD post-hoc test (p < 0.05) to assess significant differences in weight gain, survival rates, and plant biomass across treatments. Results indicated that operational costs increased with higher stocking densities, reaching $52.58 for G1, $82.90 for G2, and $113.60 for G3, despite uniform initial setup costs across all groups. Tilapia biomass exhibited a clear density-dependent increase, with final weights of 7.84 kg (G1), 13.49 kg (G2), and 20.22 kg (G3). Correspondingly, net profits rose from $5.68 in G1 to $28.10 in G3. These findings highlight the significance of strategic stocking density management in optimizing the productivity and economic efficiency of aquaponic systems. Implementing cost-effective stocking strategies and refining system design can significantly enhance the viability of aquaponics, particularly for small-scale agricultural operations.