Phenotypic variation among individuals is thought to be caused by differences in genes and/or environmental conditions. Therefore, if these sources of variation are removed, individuals are predicted to develop similar phenotypes lacking individual variation. In sharp contrast to these predictions, we find substantial individual variation in behaviour among genetically identical individuals of the clonal fish, Poecilia formosa, that were isolated directly after birth into highly standardized environments. In order to study both causes and consequences of these individual differences, we developed a biomimetic robot – the so-called Robofish – that is able to integrate itself interactively into groups of fish. I will thus showcase my research on free-living Sulphur mollies (Poecilia sulphuraria) in Mexico that indeed use several mechanisms found in laboratory experiments to perform astonishing collective behaviors when faced with real predators in their natural habitats.