Common chub, European chub, Chub
The common chub (Squalius cephalus), also known as the European chub or simply chub, is a species of European freshwater ray-finned fish in the carp family Cyprinidae, that frequents both slow and moderate rivers, as well as canals, lakes and still waterbodies of various kinds.
It is a stocky fish with a large rounded head. Its body is long and cylindrical in shape and is covered in large greenish-brown scales which are edged with narrow bands of black across the back, paling to golden on the flanks and even paler on the belly. The tail is dark brown or black, the dorsal fin is a greyish-green in colour and all the other fins are orange-red. The dorsal fin has 3 spines and 7-9 soft rays while the anal fin has 3 spines and 7-10 rays. The vertebrae count is 42-48. It can grow to 60 cm standard length but most fish are around 30 cm.
The chub is distributed throughout most of northern Eurasia, it can be found in the rivers flowing into the North, Baltic, northern Black, White, Barents and Caspian Sea basins, the Atlantic basins south to Adour drainage in France and in Great Britain north to 56°, in Scandinavia in southern Finland and southern Sweden north to around Stockholm. In the Mediterranean basin it is found in France from the Var to the Hérault, and may also be present in the Aude, drainages. It is absent as a native species from Ireland and Italy but has been introduced to both countries; in Italy S. cephalus is present and acclimatised since decades, but it seems marginally found here and there (mainly in the Po river basin), never forming well established populations.
It is most abundant in small rivers and large streams in the "barbel zone" where there are riffles and pools. It occurs along the banks of slow-flowing lowland rivers in large lake and even in mountain streams. Chub in lakes undertake spawning migrations into inflowing streams. The adult fish are solitary but the juvenile fish are sociable and occur in shoals. The larvae and juveniles prefer rather shallow habitats along shorelines and these smaller fish have a varied diet of aquatic and terrestrial animals while the large, solitary adults prey mainly on freshwater shrimp and small fishes. In the United Kingdom, chub have been recorded feeding on worms, molluscs, crustaceans, and various insect larvae while large chub eat considerable numbers of small fish, such as chub, eels, common dace, common roach, gudgeon and minnows as well as frogs, crayfish, voles and young water birds. They have also been observed eating berries such as blackberries and elderberry from trees overhanging the water. They feed throughout the year if there are opportunities, even in the coldest days of midwinter.
Spawning happens when the water temperature reaches 14 °C, and lasts from May to September. They spawn in fast-flowing water above gravel substrates but only infrequently will they spawn among submerged vegetation. The females spawn more than once during a season and each female will mate with several males. The males aggregate at spawning sites and will follow the ripe females, often with much splashing, to shallow riffles. Females lay pale yellow sticky eggs which adhere to the gravel, weed and stones in flowing water. Sexual maturity in chub is influenced by environmental factors with males reaching sexual maturity at the age of 2–4 years while females reach it at 4-6 although some individuals may mature much later than this. The fish can live for up to 22 years in the wild, where the age of fish can be assessed through by the number of rings that are visible in scales, these represent seasonal growth patterns.
Recent work has shown that chub ingest microplastic particles. Whereas many as 25% of sampled fish contained particles, these particles were not found in muscles. Many of the particles found were fibres that are released from clothes during washing, these are also ingested by macroinvertebrates such as Daphnia. Chub can also be contaminated by metal pollution such as copper, magnesium and sodium which can accumulate in tissues like the muscle, gills and liver. Young of the year fish contained particularly high levels of metal contaminants.
