Species- and diet-specific aquaculture wastewater nutrient profile: Implications for aquaponics and development of sustainable aquaponics diet

Abstract

Aquaponic (AQP) systems use aquaculture wastewater to supply the nutrients for plant growth. Recent fish meal (FM) production and price trends call for adopting of financially and environmentally sustainable protein sources for fish feed. However, different protein sources can alter the macro-and micro-nutrient effluxes from fish tanks and their nutritional value for plant growth. Early attempts to formulate the AQP diets have focused on enhancing nutrient efflux via dietary additives such as potassium diformate or potassium chloride. Here we present an alternative approach. We tested the effect of four aquafeeds differing in protein sources (complete substitution of FM with black soldier fly meal, BSFM; poultry blood meal, PBM; and hydrolyzed feather meal, HFM) on nutrient efflux in the water from Colossoma macropomum and Clarias gariepinus. The water from PBM and HFM-fed fish showed the highest efflux of TN (0.106 and 0.097 mg.L−1.g of feed, respectively), while the efflux of soluble reactive phosphorus and calcium was highest in FM-fed fish (0.012 and 0.028 mg.L−1.g of feed, respectively). BSFM-fed fish had the highest efflux of magnesium and potassium (0.008 and 0.023 mg.L−1.g of feed, respectively). Regarding macronutrients, the species-specific effects were observed only in sulphur, with higher efflux from C. macropomum. Iron efflux was not affected by diet, while higher efflux was observed in the trial with Clarias gariepinus. Effluxes of other micronutrients showed diet- and species-specific effects, except for zinc and manganese, with similar effluxes between species. In general, we found that it is possible to manipulate the nutrient efflux from RAS using alternative sustainable aquafeed components.