Familiarity effects on fish behaviour are disrupted in shoals that contain also unfamiliar individuals

Abstract Research on several social fishes has revealed that shoals constituted by familiar individuals behave remarkably differently compared to formed unfamiliar individuals. However, whether these behavioural changes may arise also in composed a mixture of and individuals, situation commonly occur nature, is not clear. Here, we observed the behaviour Mediterranean killifish ( Aphanius fasciatus ) were both (i.e. each other pairs) it with entirely made either or Shoals took longer emerge from refuge swam more cohesively fish. behaved as Moreover, mixed did segregate pairs according their familiarity. This study suggests do show effects Significance statement Laboratory studies have fish versus fish, finding notable advantages former ones, such improved antipredator foraging behaviour. comparing two opposite shoal types provide information natural situation, because often change composition. We investigated how behaved. analysed shoals’ preference for open environment covers swimming cohesion. Results showed mostly like groups might be hardly seen nature species which composition frequently.