How fish feed

Source: The Waltham Book of Companion Animal Nutrition, Pergamon Press, 1993
Fish use a whole arsenal of tricks in order to find their feed, using sound, scent, sight, touch and electro receptors, depending on the species.
Catfish have barbels which they use to find their prey. In the dark and murky waters, which form their habitat, hunting on sight is not very useful.
Killifish, on the other hand, depend on the visual aspect, although the feed intake depends on chemical receptors.
Piranhas also depend on their visual senses. They avoid feed that looks just like them.
Form, color and contrast are important factors in localizing feed and being attracted to it in the first place. It even looks as if fish have a preference for certain colors, while the contrast between the color of the feed and the background is an important factor in finding the feed. Fish that feed during the night have a way to find feed without sight. During the day, these fish are vulnerable for predators. The fish are specialized in approaching their prey as closely as possible, with the night as their cover.
When fish that are active during the day and night-feeding fish are housed together, it is important to make sure the feed is available during the day, as well as during the night, when the lights go out.

Many tropical fish are still caught in the wild. These fish do not recognize flake food or pelleted food right away. It is therefore best to feed these ‘wild’ fish live food at first, despite of the larger risk of diseases. After the fish become adapted, the wild fish will also recognize the flakes as feed. It may help to house the wild fish together with fish that are already domesticated. This way, the new fish can learn about feed from the others.