Tigger sums it up "the water in front of you"
Most important is the water clarity - Fish have eyes to see with, and a sense of smell to find food with when they can't see - for example on a moonless night or in intensely clouded water (eg carp puddles) Obviously in partially clouded water they may well use both senses.
A secondary consequence of cloudy water is the colour intensity of the roach themselves - the cloudier the water, the more anaemic* the roach - and incidentally the more likely they are to be hybrids with rudd or bream rather than true roach. So the future holds fewer brightly coloured roach from sparkling waters, and more colourless mongrels from "commercials" and similar pools.
Oh, and don't forget sound (and its partner, vibration detection) - maggots, casters, hempseed, small pellets etc will soon train roach to come up in the water to the sound of a pinch of any of those being chucked in. - and of course the sound/vibrations of other fish gobbling food from surface or rooting on the bottom will grab attention.
* yes I know the dipthong letters should joined, but I have better things to do than teach my spell-checker Anglicised Greek.