Incorporation of salmon fish feed and feces components in mussels (Mytilus edulis): Implications for integrated multi-trophic aquaculture in cool-temperate North Atlantic waters Aleksander Handå a, b, ⁎, Anders Ranheim a , Anders Johny Olsen a , Dag Altin c , Kjell Inge Reitan a, b , Yngvar Olsen a , Helge Reinertsen a a Norwegian University of Science and Technology, (NTNU), Department of Biology, Centre of Fisheries and Aquaculture, N-7491 Trondheim, Norway b SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway c Biotrix, N-7465 Trondheim, Norway abstract article info Article history: Received 21 November 2011 Received in revised form 18 September 2012 Accepted 20 September 2012 Available online 5 October 2012 Keywords: Mytilus edulis Salmon fish feed Salmon feces Fatty acids Bivalve growth Integrated multi-trophic aquaculture The incorporation of salmon fish feed and feces components in the digestive gland, mantle, and gill tissue of blue mussels (Mytilus edulis), and associated growth in shell length and soft tissue dry weight, were studied in a 28 day laboratory experiment. Mussels were fed mixed rations of either salmon fish feed and Rhodomonas baltica, salmon feces and R. baltica or mono rations of either a full or half ration of R. baltica. Feed rations were designed to supply a particulate organic carbon ration equal to ~5% of soft tissue carbon content ind -1 day -1 . Significant changes in the fatty acid composition, which appointed that of the food profiles, were evident in the digestive gland and gill tissue (p b 0.05), whereas no changes were found in mantle tissue. For digestive gland data, a principal component analysis particularly identified the contribution of 18:1 (n -9), 18:3 (n -3), 18:2 (n -6) and 20:1 (n -9) and as being the single fatty acids most responsible for the difference between the various diets. A significant growth in length was found for mussels fed fish feed and R. baltica (p b 0.05), but not for mussels fed feces and R. baltica. The dry weight was significantly higher for mussels fed the full diet with R. baltica compared to the other diets, and significantly lower for mussels fed feces and R. baltica than fish feed and R. baltica at the end of the experiment (p b 0.05). A more pronounced incorporation of salmon feed compared to salmon feces components in mussel tissues suggested that mussels will utilize fish feed more efficiently than feces particles in an integrated aquaculture with salmon. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Global salmonid production increased by ~60% from 1999 to 2009 (1.26 to 2.17 million tons) (FAO, 2011), and further growth is expected. Atlantic salmon (Salmo salar) cage aquaculture accounts for the majority of the production (1.44 million tons in 2009, FAO, 2011), and it is esti- mated that 67–84% of the nutrients (carbon, nitrogen and phosphorus) from the feed input are released into the surrounding waters as respira- tory products (dissolved nutrients), feces and uneaten feed particles (Hall et al., 1990, 1992; Holby and Hall, 1991; Troell et al., 2003 and ref- erences therein, Norði et al., 2011). Feed wastage is typically in the range of 3–5% (Cromey et al., 2002) and a feed loss of e.g. 3% will constitute about 12% of the total solid wastes from a salmon farm (Reid et al., 2008). There is an increasing concern with regard to the negative envi- ronmental impacts associated with this nutrient load (Amberg and Hall, 2008; Braaten, 2007; Tett, 2008), with one of the major challenges for the sustainable development of salmonid mariculture therefore being to minimize waste discharges that can potentially lead to deterio- ration of the local marine environment (Cheshuk et al., 2003). As a measure to reduce this organic loading it has been suggested to cultivate inorganic and organic extractive species at lower trophic levels in close vicinity to the fish farms in an integrated multi-trophic aquacul- ture (IMTA) system. IMTA has two non-conflicting overall objectives: 1) Increased biomass production and added value based on the feed investments, and 2) mitigating potentially negative environmental im- pacts of waste nutrients. In this way, IMTA may contribute to a more sustainable aquaculture production (Chopin et al., 2001, 2008; Neori, 2008; Neori et al., 2004a, 2004b; Troell et al., 2003, 2009). In a properly designed IMTA system, the dissolved nutrient wastes can be taken up by inorganic extractive species such as seaweed (Buschmann et al., Aquaculture 370-371 (2012) 40–53 Abbreviations: RB, Rhodomonas baltica; FD, fish feed; FC, fish feces. ⁎ Corresponding author at: SINTEF Fisheries and Aquaculture, Department of Marine Resources Technology, Brattørkaia 17C, N-7010 Trondheim, Norway. Tel.:+47 91577232. E-mail address: aleksander.handa@sintef.no (A. Handå). 0044-8486/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aquaculture.2012.09.030 Contents lists available at SciVerse ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online