Nutrient Utilization in a Nile Tilapia and Garlic Aquaponic System Co‐Cultivated With Microalgae

Microalgae are used in water treatment to remediate the water quality of aquaponic systems due to their remarkable adaptability. Their potential for nutrient utilization is significantly influenced by microalgae species, types of aquaponic plants, and growing conditions. This study determined the feasibility of co‐cultivating microalgae species Chlorella vulgaris and Scenedesmus sp. and blue‐green alga (cyanobacteria) Spirulina platensis in a Nile tilapia and garlic‐based aquaponic system. Four aquaponic setups were operated in parallel for 8 weeks, with each setup replicated three times. Fifty juvenile Nile tilapia (initial weight: 9.94 ± 0.03 g) were assigned to 12 experimental tanks, with integrated floating raft plant beds, biofilter substrates, and continuous recirculation via submersible pumps. In the microalgae co‐cultivated aquaponic water samples, key water quality parameters, particularly dissolved oxygen (DO), pH, and chlorophyll‐a concentration, significantly improved. The chlorophyll‐a concentration, an indicator of microalgal biomass growth, confirmed that the three microalgae species performed consistently well in each of the aquaponic systems. Microalgae co‐cultivation significantly reduced the ammonia, nitrite, and nitrate contents compared to the control (ANOVA, p < 0.05). In the final 14 days of the experiment, the total nitrogen (TN) utilization rates of the microalgae treatments were significantly different from the control, showing values of 86.9% ± 7.87% for C. vulgaris , 85.0% ± 7.30% for Scenedesmus sp., 82.0% ± 9.14% for S. platensis , and 74.4% ± 3.21% for the control (ANOVA, p = 0.0001). Similarly, the total phosphorus (TP) utilization rate was significantly higher under microalgae treatment than in the control (ANOVA, p = 0.0002): 57.8% ± 2.13% for S. platensis , 57.6% ± 4.19% for C. vulgaris , 55.6% ± 1.91% for Scenedesmus sp., and 46.6 ± 2.34% for the control. Microalgae co‐cultivation significantly improved the performance of Nile tilapia, enhancing feed intake, weight gain, feed conversion ratio (FCR), and survival, emphasizing its functional role to reconfigure nutrient partitioning and water quality regulation in aquaponics.