The bleak is a minor freshwater fish, both because of its tiny size (average 10cm/4in) and its limited distribution. However, it is important as a food source for other species and as quarry for the match angler when quantity rather than quality is the aim. It can sometimes be the only species catchable on flooded rivers. Youngsters should also have fun trying for this small but lively fish.
You can recognize a bleak by its slender, narrow, silvery body, steely blue-green back and large eyes. The delicate scales are covered in crystals of guanine, a pearl-like chemical found in animal tissue – in fact, in the 19th century bleak scales were collected to make artificial pearls.
The fish has a relatively large mouth and a protruding lower jaw, a sure sign of a surface feeder. The jaw distinguishes it from roach and dace, and it also has a larger anal fin with 16-23 rays (dace have 10-11 and roach 12-14).
Once it is out of water the bleak is rather conspicuous, but in the water its quicksilver colour matches the reflections on the surface, effectively concealing it. It feeds on insects that fall on the water, and on small crustaceans, but also searches for food throughout the water column.
Usually found in the company of roach and dace, the bleak lives mainly in rivers with a smooth but steady flow, but it is also found in stillwaters flooded by rivers (in lakes by the Thames and Trent in particular). The fish particularly favours the slack water round the mouths of lock cuttings at times of flooding and fast flow. It is not found at all in Scotland or Ireland.
Because it seldom grows to any great size, the bleak relies on safety in numbers. Though this gives it some protection, many are eaten each year by predatory fish such as pike, and by such birds as herons and kingfishers.
Like most of its fellow members of the carp family, the bleak spawns between April and June, depositing up to 8000 yellow eggs on plants and stones in both still and running water. After only a week the young hatch and begin feeding on microscopic organisms. The are rather slow-growing, and can often take up to four years to reach maximum size.
A prolific breeder, the bleak can reach plague proportions – often forming the major species in fisheries; mysteriously, it can sometimes disappear for a few years, returning as quickly as it went.