Squalius cephalus
(European chub)

The chub is a European freshwater cyprinid which has been reported as an invasive species in Italy and targeted for removal from a river system where introduced in Ireland. It is a long lived fish and has high mobility due to its pelagic condition. Humans may also facilitate its spread due to its value as a game or bait species in recreational fishing. It is also considered a valuable food resource in some regions, although the flesh is of poor quality (Dahl and Medem, 1964).

S. cephalus has ecological characteristics associated with invasiveness. It is omnivorous, and its food sources range from small (i.e. detritus, plants, invertebrates) to large (i.e. tadpoles, small fish) items. In addition it has high fecundity, fast growth rate, and is considered tolerant of anthropogenic pressures. However, there are few reports of impacts in its introduced range and indeed the changes in the taxonomic status of the species make it difficult to identify introduced populations.

Froese and Pauly (2011) describe the distribution as Eurasia: North, Baltic, northern Black, White, Barents and Caspian Sea basins, Atlantic basins southward to Adour drainages (France), Great Britain north to 56°N. Scandinavia: southern Finland, Sweden north to about Stockholm. Mediterranean basin from Var to Hérault (possibly Aude) (France) drainages. Naturally absent from Italy and the Adriatic basin. 

It is reported as introduced in Italy (Kottelat and Freyhof, 2007) and Ireland (Caffrey et al., 2008).

The chub is not of interest to the aquarium trade, but is considered a valuable food resource in some countries and also has interest as a game or bait fish species. Therefore, recreational fishing and interconnection of waterways represent the main pathways of introduction into new locations.

S. cephalus inhabits pools and tables from small to large rivers, and there are also populations described in lakes or reservoirs. Lake populations migrate to inflowing streams for spawning that preferably takes place in fast-flowing waters with gravel bottoms, rarely among submerged vegetation (Kottelat and Freyhof, 2007).

Adults are usually solitary or occur in small swarms, whereas juveniles form large swarms. Adults are usually found in pools, whereas juveniles live in very shallow shoreline habitats (Kottelat and Freyhof, 2007).

Genetics

Some genetic records were listed with the same values in the River Kupa, South Pyrenees, Yugoslavia and other unspecified localities. Haploid/gametic chromosome number (n) is 25, whereas diploid/Zygotic chromosome number (2n) is 50-50 (Al-Sabti, 1986; Klinkhardt et al., 1995; Arkhipchuk, 1999).

Reproductive Biology

Sokolov and Berdicheskii (1989) reported that spawning occurs in fast-flowing water above gravel bottom, rarely among submerged vegetation. Males reach sexual maturity at the age of 2-4 years whereas females reach it at 4-6. Maturity is influenced by environmental factors and some individuals may mature much later. Spawning takes place in May-August, when temperature rises above 14ºC. Multiple spawning is described during each breeding season. Males assemble at spawning sites and follow ripe females, often with much splashing, to shallow riffles. Females then lay sticky eggs into the gravel (Kottelat and Freyhof, 2007). Pale yellow eggs are found attached to gravel, weed and stones in flowing water (Pinder, 2001). Billard (1997) also reported eggs added to plants.

Fecundity varies seasonally and geographically. The lowest value of fecundity (1158-2050 eggs) was detected in Turkey (Ünver, 1998; Ünlü and Balci, 1993) and the highest values (100,000 eggs) were detected in Europe (Vostradovsky, 1973). Maitland and Campbell. (1992) reported the same maximum values in Western Greece and Peloponnese.

Physiology and Phenology

Tolerant of anthropogenic impacts. Further studies are required.

Longevity

S. cephalus lives up to 15 years, females longer than males (Kottelat and Freyhof, 2007). Maximum reported age is 22 years (Wüstemann, 1995)

Activity Patterns

Potamodromous species.

Population Size and Density

Abundant. Unknown population trend.

Nutrition

Feeds on a wide variety of aquatic and terrestrial animals and plant material. Large individuals are predominantly piscivorous (Kottelat and Freyhof, 2007). In the UK is recorded as feeding on worms, molluscs, crustaceans, and various insect larvae (Maitland and Campbell, 1992); large chub eat considerable numbers of small fish, such as chub, eels, dace, roach, gudgeon and minnows; also frogs, crayfish, voles and young water birds. Further information on natural food sources is as follows:

Environmental Requirements

S. cephalus prefers slow-flowing waters. Although it is considered tolerant to anthropogenic perturbations, large animals may be particularly vulnerable to reduced water flow levels due to the pelagic conditions of the species. Detailed studies on environmental preferences to establish lower and upper tolerance values have not been published. A study performed on Iberian populations of S. laietanus (i.e. formerly S. cephalus) considers the species tolerant to poor water quality and physical habitat degradation gradients (Maceda-Veiga and De Sostoa, 2011).

All piscivorous species are the chub’s natural enemies (e.g. birds, mammals, introduced and native piscivorous fish species).

Animal feed, fodder, forage

• Bait/attractant

General

• Sport (hunting, shooting, fishing, racing)

The similar morphological traits between species of the Squalius genus require the aid of specialists to distinguish between them. The combination of morphological and genetic traits may also be necessary to ensure proper identification (particularly in juvenile specimens) and this procedure may also allow detection of hybrids.

The existence of stowaway species mixed with valuable species in ornamental or any other live fish stocks is not uncommon. The live fish trade therefore requires careful inspection by specialists in order to detect undesirable organisms which are often not labeled. In addition, the regular monitoring of current waters allows managers to detect new fish introductions and to know the spread patterns of exotic species once introduced. This information helps resource managers to identify areas at high risk of invasion and to plan local eradication programs when possible. Electrofishing is a widely recognized method to catch fish without damaging the ecosystem. Nets are a complementary sampling tool for surveys performed in lakes or reservoirs.

Differs from its congeners in France, North, Baltic, Arctic, Black and Caspian Sea basins by possession of the following characteristics: dorsal profile with a well-marked discontinuity between head and trunk; a row of black pigments along free margin of each flank scale, forming a regular reticulate pattern, with no or very few pigments on central part of scales; anal and pelvic fins orange to red; dorsal fin with 8½ branched rays; anal fin with 8½ branched rays (rarely 9½); scales on lateral line 40-45 + 2-3; mouth terminal, with well-marked chin; lower jaw tip not included in the upper lip; interorbital distance 37-42% HL; postorbital distance 47-51% HL; eye diameter 17-22% HL, 1.5-2.3 times in snout length; body depth 22-27% SL; lower jaw long, length greater than depth of operculum; iris whitish; pharyngeal teeth 2,5-5,2; in stretched anal fin of individuals larger than about 15 cm SL, distance between tips of first and last branched rays usually greater than caudal peduncle depth. Size up to at least 600 mm SL (Kottelat and Freyhof, 2007). Caudal fin with 19 rays (Spillman, 1961).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Education programmes can be used to raise public awareness about the threats of introduced species to ecosystems. Regular monitoring of waters by trained specialists can be used to detect new invaders and newly invaded areas.

Eradication

Once established, complete eradication is almost impossible, particularly in large areas. Local extirpation of introduced fish species may be performed in areas of high conservation value, particularly in small streams where the probability of success increases. In the River Inny, Ireland, a netting and electrofishing campaign has been running since 2006 to control a small number of introduced chub (Caffrey et al., 2008) with the result that none have been detected since 2010 (J Caffrey, Inland Fisheries Ireland, personal communication, 2012).

Control

Physical barriers and rotenone are commonly used to control small fish. Regular removal of specimens in small streams may mitigate the effect of exotic species.

Monitoring and Surveillance

Regular electrofishing surveys.

Italy: FAO (Food and Agriculture Organization of the United Nations), Viale delle Terme di Caracalla, 00100 Rome, http://www.fao.org/

04/01/12 Original text by: 

Mònica Utjés Mascó, Department of Animal Biology & Research Institute of Biodiversity (IrBio), Faculty of Biology, University of Barcelona, Avda Diagonal, 643. E-08028 Barcelona, Spain

Alberto Maceda Veiga, Department of Animal Biology & Research Institute of Biodiversity (IrBio), Faculty of Biology, University of Barcelona, Avda Diagonal, 643. E-08028 Barcelona, Spain

The names of reviewers are available from CABI on request.