Predators such as pike often hunt by sight so their eyes are set well forward and close together on the head. This produces a large area of overlap between the eyes, givion. The area covered by both eyes is a small zone directly in front of the fish. This zone is well served with sight receptors in the eye, but outside it details are blurred, and only movements can be accurately detected. You are much more likely to spook fish if you are moving.
Fish may not have huge brains, but they are well adapted to life in water. They are highly capable of spotting danger and food, which makes them possible to catch but also alerts them to our presence. Like humans, most fish can see, smell, taste and feel – and some can hear. However, living in water, they tend to do it differently.
How fish see
Water absorbs and warps light far more than air, especially in murky conditions. For this reason sight is often less useful under water – most fish are quite short-sighted and can’t see as well as land animals.
Fish eyes are positioned on the side of the head, giving all-round vision. However, to be able to judge distances properly, both eyes must be able to focus in the same direc- ing good distance perception, and allowing them to home in on prey fish. For shoaling fish such as roach, distance vision is less important, and the eyes are well apart on either side of the head. This gives them a very wide field of view in which they can detect movement – useful for fish that need to follow a shoal and also avoid the attentions of fast-moving predators.
Water doesn’t transmit light very well, but it is an excellent medium for smell. Most fish have a well-developed sense of smell, located in two nostrils on either side of the snout. Wels have very sensitive nostrils and hunt mainly using this sense — one reason they have such small eyes. Taste buds are not restricted to the fish’s mouth. Catfish are able to distinguish food from inedible substances through their skin. Many fish have taste buds in barbels (feelers) which they use for detecting and tasting food before eating it. The skin is sensitive, so keep handling to a minimum – at best it is unpleasant for the fish.
The lateral line is very sensitive to vibration through tiny openings. With this sense organ fish can pick up movements in the water, helping them avoid enemies and find food. As water transmits vibrations so well, a careless footfall can alert fish over a wide area to your presence.