INTRODUCTION
In the upper pelagic habitat, visual predators flourish; places to hide are almost non-existent and other means are necessary to become inconspicuous. One essential characteristics of pelagic habitat is the changing light conditions with depth and time. And as light conditions in the water column change, so do the optimal anti-predation mechanisms (Johnsen, 2002). For a given species, this may be reflected in size by depth and time, feeding by depth and time, and colour by depth and time.