Unless you are one of those dedicated fishermen who, armed with polaroid glasses, landing nets and fishing rods, have insights into what is going on beneath the water surface, most of us have little contact with freshwater fish and know little of their world. More’s the pity, since most fish are inherently beautiful and move around in water with grace and agility. However, the excitement of watching fish swim about is evident from visiting an aquarium, although sadly few of our freshwater fish regularly feature in these collections.

To live in a fish’s world means swapping around some of our senses. Highly sensitive to vibration, they live in a sound-depleted world. Their vision is good but not spectacularly so, but their master sense is smell. One glance at a fish’s brain reveals moderately sized optic lobes controlling vision, but very large olfactory lobes regulating smell. For example, it is now clear that Atlantic salmon find their way back to the location of their birth from the ocean feeding grounds partly by using information from the Earth’s magnetic field, but chiefly by smell. Tiny concentrations of the molecules in the fresh water of their natal stream can be detected in the huge dilution of the estuary mouth, enabling the fish first to find the correct river and then to navigate up the river system to find what may be the tiny tributary of their birth. Species such as carp also use smell extensively in prey and food location – hence the huge range of baits used by carp fishermen.