The stone loach (Barbatula barbatula) is a freshwater fish of the genus Barbatula of the family Carpidae. Length 40-60 cm, sometimes up to 90 cm, weight 2-3, rarely up to 10 kg. It lives in the waters of Central Europe, South and Central Asia. Prefers fast, clear water. It is not found in lakes and other standing waters. It reaches sexual maturity at the age of 4 years. Spawning is batch spawning, in May-June at water temperatures not lower than 15°C. Eggs hatch in areas with fast currents, on sandy and stony bottoms. Fecundity does not exceed 8,000 eggs. Bentophagous. Of local commercial importance.
Leads a benthic life. It prefers small, fast-flowing rivers with sandy or gravelly bottoms, but can also be found in the lower reaches of some large rivers, in lakes and brackish waters of the Gulf of Finland, in reservoirs and ponds. It is equally at home in cold spring springs and in the tingling warm waters of artificial ponds, where it can sometimes reach huge numbers. In winter it burrows in the mud and can survive for a long time on wet ground when the water is dry. It feeds on aquatic invertebrates, insect larvae, plants and fish eggs.
The scales of the stone loach are separate and do not overlap. The dorsal and anal fins are short, the caudal fin is truncated, sometimes with a slight notch, in large individuals the edges are slightly rounded. The head is slightly flattened from top to bottom, the mouth is turned downwards, the upper lip has four densely packed antennae, with one more antennae in the corners of the mouth. The colouration is very variable and depends both on the age of the fish and the place where it lives. In rivers with sandy and stony bottoms, fish will always be lighter and more yellowish than in non-flowing, tinny places. Young fish are much more colourful than old fish, and fish living in the south are slightly darker than those living in the north. Usually the back and sides of the body are greyish-yellow with greenish-brown spots of various shapes and sizes, sometimes merging into a broad longitudinal band along the side or forming transverse stripes, from the lower edge of the eye to the base of the middle antennae is a dark stripe, a blackish elongated spot is located at the base of the caudal fin. All fins are mottled with rows of dark spots, sometimes forming continuous stripes, and only the pelvic and anal fins are usually yellowish-white without spots.
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