Shoaling preferences in banded killifish differ in shoal species composition, shoal size, and individual body size within the shoal. The shift in preferences is triggered by predatory stimuli. In the presence of predatory stimuli, a banded killifish individual will prefer the bigger conspecific shoal, but only as long as the shoal is homogenous in individual fish size. If the size of individual fish were different, they would join a shoal of similarly sized fish regardless of shoal size. This preference is maintained by predatory threat. Body size is a more significant determinant of shoaling preference than shoal size and species composition.