IMO it depends on the fish, fish from darker climes may rely more on smell fish from clearer waters more on sight while both are important, most fish we find in our reefs come from well lit reefs so mostly it would be sight. I cant even count the times my fish have seen something floating buy to suck it up then spit it out because it was inedible. Sight more than smell for the most part though smell is a good enticer to attract an otherwise uninterested fish to food.