Tropical fishes recruiting to temperate regions outside their native range (termed vagrants) provide an exciting opportunity to investigate behavioural interactions between tropical and temperate species and how these will be impacted by climate change. For gregarious vagrants, the formation of mixed-species shoals with native heterospecifics may provide benefits in terms of predation avoidance and foraging efficiency in novel temperate environments. Each year, small numbers of larval Abudefduf vaigiensis (Indo-Pacific Sergeant) are transported southwards from the coral sea, settling in sheltered embayment’s on the temperate coast of south-eastern Australia. To evaluate the extent to which mixed-species shoaling behaviour facilitates the growth and survival of vagrant A. vaigiensis, I have conducted visual surveys and in situ behavioural observations along with laboratory-based shoal choice experiments. I have then modelled the influence of key factors, namely shoal composition, water temperature and habitat type, on shoaling behaviour. Results revealed that 68% of shoals contained multiple species and A. vaigiensis displayed preference larger mixed-species shoals when under predation threat and when in exposed habitats. These findings provide broad support for the importance of mixed-species shoaling behaviour and exemplify how novel behavioural interactions between tropical and temperate species may structure the redistribution of fishes with climate change.