Evaluating the Effects of a Short-Term Feed Restriction Period on the Behavior and Welfare of Atlantic Salmon, Salmo salar, parr Using Social Network Analysis and Fin Damage

Social network analysis (SNA) was used to quantify the role of behavioral interactions on the frequency and severity of fin damage in Atlantic salmon, Salmo salar, parr subjected to a short feed restriction period of 10 d. Dorsal fin erosion was observed in both feed-restricted (FR) and control (C) groups of fish, but was significantly more frequent and severe in FR groups. FR fish had a significantly lower weight, length, and poorer body condition in comparison to C groups. Social networks based on aggressive interactions showed significantly higher overall degree-centrality, clustering coefficients, out and in-degree centralities in FR groups. This led to the formation of clusters of fish into initiators and receivers of aggression. Only the receivers of aggression exhibited dorsal fin damage, while initiators did not. Initiators and receivers of aggression in FR groups retained their roles even after control conditions were restored, suggesting that short periods of feed restriction can lead to permanent modifications in aggressive behavior. This study demonstrates the applied value of using SNA to investigate the longer term effects that aggressive behavioral interactions have on fin damage and welfare in Atlantic salmon.