Optimizing nutrient utilization, hydraulic loading rate, and feed conversion ratios through freshwater IMTA-aquaponic and hydroponic systems as an environmentally sustainable aquaculture concept

Abstract

Water quality in land-based fish production can be controlled through either instantaneous water exchange or costly wastewater treatment followed by recirculation. Agricultural-aquaculture integration is an excellent alternative technique for reducing nutrient discharge levels, boosting profitability, and converting fish culture wastewater into valuable products. The current study employed a solar energy system to power two separate IMTA-aquaponics systems (Nutrient Film Technique, NFT, and Floating Raft Systems, FRS) for the cultivation of Nile tilapia, African catfish, thin-lipped grey mullet, freshwater crayfish, freshwater mussels, and a variety of vegetables. Tilapia and catfish were fed exclusively on diets under the IMTA system. All wastewater from tilapia and catfish ponds, both dissolved and solid, flows sequentially to ponds containing other cultivated species. The water then flows through the IMTA system's terminal point to the NFT and FRS systems before returning to the tilapia and catfish ponds, allowing complete control of the nutrient flow throughout this entire circular system. Two 147-day production cycles were concluded. The results from the second production cycle are reported. Total biomass gain for aquatic species in the IMTA system was 736.46 kg, compared to 145.49 kg in the tilapia and 271.01 kg in the catfish monoculture systems. The current IMTA system had a cumulative feed conversion ratio (FCR) of 0.90, while the FCRs for tilapia and catfish were 1.28 and 1.42, respectively. Nile tilapia and catfish consumed 571.90 kg of feed containing 25.70 kg of nitrogen (N) and 9.70 kg of phosphorus (P), reflecting, and gaining 11.41 and 3.93 kg of dietary N and P, representing 44.40 and 40.46% dietary N and P retention, respectively. In the IMTA system, the addition of mullet and prawn as detrivores aquatic animals improves dietary N and P utilization efficiency to 59.06 and 51.19%, respectively, while the addition of mussels as herbivore animals improves dietary N and P utilization efficiency to 65.61 and 54.67%, respectively. Finally, using FRS and NFT as hydroponic systems increased dietary N and P efficiency to 83.51% N and 96.82% P, respectively. This study shows that the IMTA-Aquaponic system, as a bio-integrated food production system, can convert the majority of fish-fed residues into valuable products suitable for desert, rural, and urban areas in impoverished and developing countries.