The prominent stripes on the back of mackerels seemingly are there to provide camouflage against broken backgrounds. That is not the case, though, because mackerel live in midwater pelagic environments which have no background. However, fish have an optokinetic reflex in their visual systems that can be sensitive to moving stripes. For fish to school efficiently, they need feedback mechanisms that help them align themselves with adjacent fish, and match their speed. The stripes on neighbouring fish provide "schooling marks", which signal changes in relative position.