“…Animals may associate through active preference; shoaling fishes have been shown to form associations based upon a range of factors including body size (Ward & Krause, ; Croft et al, ), relatedness (Frommen & Bakker, ; Frommen et al, ; Piyapong et al, ), familiarity (Griffiths & Magurran, ; Croft et al ., ; Frommen & Bakker, ; Ward et al, ), chemical cues derived from similar diet or habitat use patterns (Ward et al, , , , ; Webster et al, , , b; Kleinhappel et al, , ) and competitive ability (Metcalfe & Thomson, ). Assortment may also arise passively through shared habitat preference or site fidelity (Croft et al, ; Webster et al, ; Ward et al, ), similar swimming speeds (Krause et al, ) or similar patterns of activity, risk aversion or cover use linked to personality traits (Pike et al, ; Croft et al, ). The processes or mechanisms behind the positively correlated association patterns seen in this study are not clear; many of the above factors known to affect group composition, such as size, familiarity and habitat and diet use background were held constant as far as possible in our study and are therefore unlikely to be responsible.…”