Loach  (Cobitis calderoni)

Classified as Endangered (EN) on the IUCN Red List (1).

This small, bottom-dwelling member of the loach family has an elongated, cylindrical body, covered with indistinct round scales and marked with rows of black spots, which are largest towards the underside. The base of the tail is very long and narrow, and the dorsal fin is located towards the rear of the body. The mouth is situated below the head, and is surrounded by three pairs of fleshy barbels, and, as in many loaches, Cobitis calderoni has a split, erectile spine below the eye, used in defence against predators (2) (3) (4). Male and female Cobitis calderoni are similar in appearance (2) (3).

Cobitis calderoni is one of three endemic Iberian loaches, and is restricted to the Duero, Ebro and Tajo river basins of northern Spain and Portugal (1) (2) (3) (5) (6).

This loach inhabits the upper and middle reaches of rivers, where dissolved oxygen levels are higher, and prefers to live in clear, shallow water with a gravel or stony bottom (1) (2) (3) (6). Records of its occurrence in reservoirs need confirmation (7).

Relatively little is known about the biology of Cobitis calderoni. A rather short-lived fish (8), it feeds mainly on aquatic invertebrates, including fly larvae and tiny crustaceans, as well as on unicellular algae (9). Spawning occurs in spring, between March and May (2) (3) (10), the female selecting a gravel bottom with strong currents, and using the tail fin to dig a trench into which around 200 large eggs are deposited (2) (3). Cobitis calderoni is reported to form distinct pairs during breeding, and to live for up to three years (8).

Cobitis calderoni has declined in abundance and range in recent decades, and has now disappeared from parts of the Duero and Ebro rivers, with remaining populations also becoming more fragmented. The main threats to the species include gravel and water extraction, water pollution, dam construction, the destruction of spawning areas, and the introduction of exotic fish such as pike (Esox lucius), which may act as predators, competitors, or vectors of disease (1) (2) (3) (6) (7). The decline in the Cobitis calderoni population is predicted to continue at the current rate, putting the species at ever-increasing risk of extinction (1).

Cobitis calderoni is listed as Vulnerable in the Spanish Red Data Book (3), and as Endangered in the Portuguese Red Data Book (7), and is on Annex III of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention) (11). No specific conservation measures are known to be in place for the conservation of this small loach (3), but recommended actions include effectively controlling non-native fish introductions, controlling gravel extraction, protecting the areas of river in which the species lives, undertaking further research into its distribution, biology and ecology, and seeking to minimise the impacts of water extraction and pollution on the aquatic ecosystem (2) (3) (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

To find out more about Cobitis calderoni see:

• Perdices, A. and Doadrio, I. (1997) Threatened fishes of the world: Cobitis calderoni Bacescu, 1961 (Cobitidae). Environmental Biology of Fishes, 50: 148.
• FishBase:
  http://fishbase.org.cn/summary/SpeciesSummary.php?id=9957
• Spanish Red Data Book - fish (in Spanish):
  http://www.mma.es/portal/secciones/biodiversidad/inventarios/inb/atlas_Peces/index.htm