Aquaponics offers a sustainable approach to food production by integrating aquaculture and hydroponics. It allows food production on non-agricultural land, increases resource efficiency, and reduces waste compared to traditional farming practices. However, increasing aquaponics productivity poses a significant challenge, as it requires maintaining a balance between fish and plant populations. Stocking density is one of the most critical factors influencing nutrient balance and water quality which directly affect system productivity. Aside from improving productivity, diversifying aquaponics products offers a promising avenue to contribute to the industry’s growth. Microalgae is widely considered a high-value culture species in aquaculture because of its diverse applications, including serving as a functional food, source of nutraceuticals, potential for biofuel and biogas production and as a highly nutritious feed ingredient for fish and livestock. The objective of the study was to incorporate algae as a component of aquaponics system and evaluate the impact of varying stocking densities of fish on the overall system productivity, including algal biomass, fish growth and plant yield. Additionally, the experiment also assessed the nutritional profile of the algae to provide insights on its potential application to various industries and examine how different stocking densities affect its nutrient composition.
Four fish densities were tested; 10 kg/m3, 20 kg/m3, 30 kg/m3, and, 40 kg/m3. Growth parameters from fish, lettuce and algae and water quality parameters were measured after 35 days of culture. The results indicated that after four batches of algae culture, the highest stocking density (40 kg/m³) produced significantly higher algae biomass yield compared to the lower stocking densities (10 kg/m³ and 20 kg/m³). An increasing trend in biomass yield was observed as stocking density increased. Increasing trend with stocking density was also observed in fish total biomass as well as in wet and dry weights of lettuce. The increased algae biomass and lettuce yield can be attributed to the elevated levels of important nutrients crucial for their growth such as nitrate, phosphate and potassium. Lettuce micronutrient analysis revealed that higher fish densities generally led to reduced nitrogen, nitrate and magnesium content, while manganese content increased significantly. The findings demonstrated that increasing fish densities to 30,and 40 kg/m3 significantly improved the productivity of algae, fish and lettuce. The study also highlights the potential of incorporating algae into aquaponics systems as an additional component to enhance the value of production.