Applied Animal Behaviour Science 127 (2010) 139–151 Contents lists available at ScienceDirect Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim Social network analysis of behavioural interactions influencing fin damage development in Atlantic salmon (Salmo salar) during feed-restriction Hernán Alberto Ca ˜ non Jones a,b,∗ , Linda A. Hansen c , Chris Noble c , Børge Damsgård c , Donald M. Broom b , Gareth P. Pearce a a Wildlife Health, Fish & Conservation Medicine Group, Department of Veterinary Medicine, University of Cambridge, United Kingdom b Centre for Animal Welfare and Anthrozoology, Department of Veterinary Medicine, University of Cambridge, United Kingdom c Nofima Marine, Tromsø, Norway article info Article history: Accepted 10 September 2010 Keywords: Social network Salmon Fin damage Aggression Welfare abstract The role of behavioural interactions in the development of fin damage amongst Atlantic salmon (Salmo salar) undergoing feed-restriction was investigated using social network analysis. Dorsal fin damage, particularly erosion, was seen only in groups subjected to feed-restriction. The amount of dorsal fin damage was positively correlated with aggres- sion and fin-biting. Feed-restricted fish exhibited significantly lower weight gain, reduced growth-rate and body condition but no differences in total length. Social networks based on aggressive interactions in feed-restriction groups showed significantly lower distance, and higher density, higher clustering coefficient and higher in and out degree centrality. These findings indicated higher and more intense aggressive interactions in feed-restricted fish. A distinctive separation of roles according to aggression was found in feed-restriction groups where initiators had high out-degree centrality and receivers had high in-degree centrality. Fish initiating aggressive interactions had less fin damage, gained more weight and attained more central positions within the school. Fish receiving aggression had more fin damage and gained less weight. Association networks in the feed-restricted groups had significantly lower values for transitivity and distance with a tendency for higher centrality. These findings indicate higher levels of interaction and an imbalance in their relationships. We demonstrated the value of social network analysis in investigating behavioural inter- actions associated with aggression and the development of fin damage in Atlantic salmon. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Fin damage is increasingly being used as a potential indicator of the welfare of farmed fish (Ashley, 2007; Broom, 2007; Broom and Fraser, 2007). It has been asso- ∗ Corresponding author at: University of Cambridge, Department of Veterinary Medicine, Madingley Road, CB3 0ES, Cambridge, United King- dom. Tel.: +44 01223 364958; fax: +44 01223 337610. E-mail address: hac39@cam.ac.uk (H.A. Ca ˜ non Jones). ciated with inter-fish competition as a result of inadequate housing and husbandry conditions, both of which are known to influence fish welfare. Fin damage can be caused by increased aggression in both steelhead trout (Salmo gairdneri) and Atlantic salmon (Salmo salar)(Abbott and Dill, 1985; Turnbull et al., 1998) and the tissue damage can be maintained and aggravated by other risk factors such as poor water quality resulting mainly from high ammo- nia and low dissolved oxygen levels (Person-Le Ruyet et al., 2008). Although the effect has not been fully eluci- dated, fish stocking densities have been also implicated 0168-1591/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2010.09.004