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Sustainability 2018, 10(6), 1805; https://doi.org/10.3390/su10061805

Commercial African Catfish (Clarias gariepinus) Recirculating Aquaculture Systems: Assessment of Element and Energy Pathways with Special Focus on the Phosphorus Cycle

1
Department of Aquaculture and Sea-Ranching, Faculty of Agricultural and Environmental Sciences, University of Rostock, 18059 Rostock, Germany
2
Marine Geology, Leibniz Institute for Baltic Sea Research, IOW, 18119 Rostock, Germany
3
Department of Waste and Resource Management, Faculty of Agricultural and Environmental Sciences University of Rostock, 18059 Rostock, Germany
These authors contributed equally to this study.
*
Author to whom correspondence should be addressed.
Received: 1 April 2018 / Revised: 23 May 2018 / Accepted: 28 May 2018 / Published: 30 May 2018
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Abstract

The reuse of effluent waters and sediments from African catfish (Clarias gariepinus) recirculation aquaculture systems requires a deeper understanding of the nutrient and energy flows and material pathways. Three semi-commercial systems, differing in stocking density, were sampled for nutritive and pollutant elements of the input- (tap water, feed) and output pathways (fillet, carcass, process water, sediments) by ICP-OES/MS and calorimetry. Highly water-soluble elements, e.g., potassium, accumulated in the water, whereas iron, copper, chromium and uranium where found in the solids. Feed derived phosphorous was accounted for, 58.3–64.2% inside the fish, 9.7–19.3% in sediments, and small amounts 9.6–15.5% in the process waters. A total of 7.1–9.9% of the feed accumulated as dry matter in the sediments, comprising 5.5–8.7% total organic carbon and 3.7–5.2% nitrogen. A total of 44.5–47.1% of the feed energy was found in the fish and 5.7–7.7% in the sediments. For reuse of water and nutrients in hydroponics, the macro-nutrients potassium, nitrate, phosphorus and the micro-nutrient iron were deficient when compared with generalized recommendations for plant nutrition. Low energy contents and C/N-ratio restrict the solely use of African catfish solids for biogas production or vermiculture. Using the outputs both for biogas supplement and general fertilizer in aquaponics farming (s.l.) (combined with additional nutrients) appears possible. View Full-Text
Keywords: African catfish; recirculating aquaculture systems; mass balance; phosphorus; nutrients; pollutants; energy; solid wastes; aquaponics; circular economy African catfish; recirculating aquaculture systems; mass balance; phosphorus; nutrients; pollutants; energy; solid wastes; aquaponics; circular economy
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Strauch, S.M.; Wenzel, L.C.; Bischoff, A.; Dellwig, O.; Klein, J.; Schüch, A.; Wasenitz, B.; Palm, H.W. Commercial African Catfish (Clarias gariepinus) Recirculating Aquaculture Systems: Assessment of Element and Energy Pathways with Special Focus on the Phosphorus Cycle. Sustainability 2018, 10, 1805.

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