Plant nutritional value of aquaculture water produced by feeding Nile tilapia (Oreochromis niloticus) alternative protein diets: A lettuce and basil case study

Societal Impact Statement Refining circular multitrophic food production methods, which integrate plant, fish, and insect outputs, is imperative for environmental sustainability. Our findings suggest that the right protein choices in fish feed, like black soldier fly meal and poultry meal, can notably enhance the nutrient profile of fish waste water. This, in turn, is conducive for hydroponic cultivation, enhancing the nutritional attributes of plants like basil and lettuce. As we reduce environmental impact and optimize resource use, it is evident that our food ecosystems are deeply intertwined. Harnessing these synergies could redefine our approach to food production, paving the way for a more sustainable global future. Summary Optimization of nutrient use efficiencies in circular multitrophic food production systems (i.e., plant, fish, and insect production) is crucial for sustainability. This study tested how protein ingredient choice in fish feed influences the plant nutritional value of the fish waste water when used for hydroponic crop production. Waste water samples were obtained from recirculating aquaculture systems (RAS) in which Nile tilapia (Oreochromis niloticus) were fed different single protein source diets—black soldier fly meal (BSFM), poultry by-product meal (PM), poultry blood meal (PBM), and fish meal. Water was analyzed for plant nutrients and used for lettuce and basil cultivation to evaluate their suitability for hydroponic crop production—viz. yield, mineral nutrient, and selected secondary metabolite levels. BSFM RAS water had the highest concentrations of K, Mg, and micronutrients (Cu, Mn, Mo, Zn) of the RAS waters, whereas PM RAS water contained the highest P concentration and had a mean pH of 6.5 closer to the optimum pH for hydroponic plants. These RAS waters consequently lead to the highest yields in basil and lettuce indicating the importance of the aforementioned factors. From a plant production perspective, BSFM appears promising as a protein source in fish feeds for aquaponics. Usage of RAS waters for plant production helps reduce (i) environmental impact of RAS water and (ii) resource input in plant production. Longer term RAS trials should be conducted to determine the maximum nutrient concentrations achievable during fish production with diets including BSFM as the main protein source.