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Effects of Ortho-Phosphate on Growth Performance, Welfare and Product Quality of Juvenile African Catfish (Clarias gariepinus)

1
Professorship Aquaculture and Sea-Ranching, Faculty of Agricultural and Environmental Sciences, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany
2
Leibniz Institute for Farm Animal Biology (FBN), Wilhelm-Stahl-Allee 2, 18196 Dummerstorf, Germany
*
Author to whom correspondence should be addressed.
Received: 28 November 2018 / Revised: 9 January 2019 / Accepted: 14 January 2019 / Published: 23 January 2019
(This article belongs to the Special Issue Welfare of Cultured and Experimental Fishes)
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Abstract

Ortho-phosphate inside recirculation aquaculture systems is limited as a consequence of precipitation and regular water exchange rates. To improve plant growth in coupled aquaponics, phosphate fertilizer addition to hydroponics can increase PO43−-P concentrations inside the process water. We investigated the effects of four PO43−-P concentrations (<10 (P0), 40, 80, 120 mg L−1) in rearing water on growth performance, feed efficiency, and welfare traits of juvenile African catfish (Clarias gariepinus Burchell, 1822). By trend, optimum specific growth rate of 2.66% d−1 and feed conversion ratio of 0.71 were observed at 40 and 80 mg L−1 PO43−-P. Higher PO43−-P significantly affected skin coloration, swimming activity and external injuries, with the palest and inactive fish combined with most external injuries in the P120 group. Mineral and protein contents in the fish remained unaffected, while fat content inside the fillets enriched with increasing PO43−-P. Inorganic P in blood plasma increased significantly, while phosphate concentrations inside the fillet remained unchanged. We suggest that PO43−-P concentrations of 40 to 80 mg L−1 do not reduce the performance of African catfish aquaculture, while increased values of 120 mg L−1 affect fish welfare. This allows limited addition of PO43−-P fertilizer in coupled aquaponics with African catfish to support plant growth.
Keywords: African catfish (Clarias gariepinus); growth; feed efficiency; elevated phosphate concentrations; welfare African catfish (Clarias gariepinus); growth; feed efficiency; elevated phosphate concentrations; welfare
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Strauch, S.M.; Bahr, J.; Baßmann, B.; Bischoff, A.A.; Oster, M.; Wasenitz, B.; Palm, H.W. Effects of Ortho-Phosphate on Growth Performance, Welfare and Product Quality of Juvenile African Catfish (Clarias gariepinus). Fishes 2019, 4, 3.

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