People's responses to social situations varies considerably according to their personality type. We span the spectrum from loners to social butterflies and everything in between. And the same is true of other animals. Depending on their lifestyle, they may either be stressed or fulfilled by socializing. Megan Currier and colleagues from Widener University in Pennsylvania, USA, aimed to better understand this idea in wild animals by measuring the energy costs associated with movement in cooperative, socialite fish or antagonistic, loner fish.