In many ways chub look like dace at first glance. Both have black tails and grey or green backs. Chub, however, usually have brassy coloured flanks, orange anal fins and big mouths, and they grow much larger than dace. Their dorsal fins are convex (arched) while those of the dace are slightly indented (concave).
Small chub of 3in (7.5cm) or so eat large invertebrates, worms and fry (recently hatched spawn). Chub are omnivorous; that is, they eat fish, insects and vegetable matter (such as silkweed, berries and bread). In fact, if an elderberry tree is overhanging a river bank, for example, chub often gorge themselves with ripe berries. Fish of over 3 lb (1.4kg) may eat small bullheads, minnows, roach and dace. They don’t have teeth in their mouth; their mighty pharyngeal teeth, located at the base of the throat, can crush just about any food item. This includes crayfish which, despite their hard shell, are quickly demolished.
Running water is the best place to look for chub – especially in any steady-flowing low- land or middle reach of river. They don’t thrive in upland waters, which are more suited to trout, salmon and grayling. Chub are a retiring fish, and they rely much on the shelter of overhanging trees, rafts of debris, underwater weeds and undercut banks -cover is an essential part of their habitat.
During the afternoon, however, chub often sun themselves. You can see them on clear, windless summer days, but be careful when approaching them, for they spook easily. They may also spook if you try to cast directly above them. Casting a yard or so upstream and in front of the fish often does the trick.
Because chub are adaptable, they can also survive in still waters; it’s here where they grow fat as barrels. Crystal-clear gravel pits contain many large specimens. On shallow gravel bars between 30-90cm (1-3ft) deep you can find them basking in the sun.
Chub usually spawn between April and June, depending on the temperature of the water. The adults swim upstream to shallow gravelly runs and breed only in flowing water. Each female can shed up to 100,000 eggs over gravel, weeds or debris on the river bed. After eight to ten days the eggs hatch. The fry feed in shoals on microscopic organisms (plankton). As they grow, they remain in shoals. Even the mature fish group together. Only the very large fish become solitary.