Minnows are such small fish – 5-6cm (2/4 in) long – that they aren’t important to the average angler, unless he uses dead ones for bait, or to youngsters who train on them. All the same, their veiy abundance in small streams makes them vital to freshwater ecology. Minnows are also a ‘barometer’ for clean water – if they disappear from a stream, it’s likely that the water quality has deteriorated.
Cousin to the carp
Within the carp family to which it belongs, the minnow is distinctive. It is slender-bodied, with a small blunt head and rather thick fleshy lips on its crescent-shaped mouth. Its scales are minute (only the tench has scales of a comparable size).
Most of the year the minnow’s belly is creamy and its back and sides are olive brown with a series of dusky blotches on the sides. But in late spring and early summer the males develop a jet black patch on the throat, and a brilliant red belly. They also have a pearly white patch at the base of each pectoral fin – these show as conspicuous white flashes as they swim.
Follow the feeding
Essentially the minnow is a fish of small, clear streams which are usually well-oxygenated and fairly warm in summer. However, they do live in large natural lakes such as Windermere in the Lake District (although they were probably introduced there in the first place.) It is also possible to catch minnows in large rivers, but these are likely to be wanderers – perhaps coming from a nearby tributary stream.
As you would expect, such small fish eat only small prey. Much of their diet when adult consists of small insect larvae and crustaceans, but they also eat plant matter and large quantities of creatures such as aphids and spiders, which blow into the water from fields and banks.
Spawning and shoaling
Spawning occurs in early summer between mid May and July. The fish gather in large shoals on shallow gravel river bottoms, especially at dusk or dawn, when the shallows seem to be filled with active, darting little fish and the white pectoral fin patches of the males appear luminous.
The eggs stick to stones, often dropping into the gaps in the gravel, and hatch in four to eight days. The hatchlings are about 5mm long. Most spawn in their third year (and few live much longer) but those that hatch early, especially if they live in the warmer streams of southern England, may spawn at the end of their first year.
In general, minnows are not solitary fish. They have a shoaling life-style. Near spawning time they can be seen ‘streaming1 through the shallows or forming a great mass in the river bed.
Minnows have a particularly refined sense of smell for the ‘alarm substance’. The skin of an injured minnow gives off a substance which others in the shoal can detect within seconds of the injury taking place. Their normal reaction is to become nervous and dart about, but if the substance continues to reach them, the shoal takes fright and dashes off.