Southwestern arched-mouth nase  (Iberochondrostoma almacai)

The southwestern arched-mouth nase is classified as Critically Endangered (CR) on the IUCN Red List (1).

First described as a new species in 2005, the southwestern arched-mouth nase (Iberochondrostoma almacai) is a small, relatively slender fish that is endemic to the Iberian Peninsula (2). It has a fairly small head and a downturned mouth which, as its common name suggests, is slightly arched (2) (4).

The body of the southwestern arched-mouth nase is light brown, with paler underparts and some darker pigmentation on the back. The fins are greyish, and there is a conspicuous, dark lateral line. The dorsal fin and anal fin of the southwestern arched-mouth nase are similar in size, and both have a slightly convex outer margin (2) (4). The dorsal fin is positioned about midway along the back, above or slightly behind the end of the pelvic fins. The tail fin has two rounded lobes (2).

The southwestern arched-mouth nase was previously classified together with the closely related Portuguese arched-mouth nase, Iberochondrostoma lusitanicum. The two species are very similar in appearance, but the southwestern arched-mouth nase has a smaller head, relatively longer snout and larger eyes. It can also be distinguished on the basis of differences in its scales, gills and ‘pharyngeal teeth’ (modified bones in the throat, used to process food) (2) (3) (4).

The southwestern arched-mouth nase is found only in south-western Portugal, in the Mira, Arade and Bensafrim river drainages (1) (2) (3) (5).

This fish inhabits small- to medium-sized streams with clear waters and low to medium currents. These streams are typically quite seasonal, meaning that the southwestern arched-mouth nase may be restricted to small pools during summer (1) (2) (3).

This species is often found in deep, sheltered areas with relatively warm water temperatures (4) (5) (6), but it usually spawns in shallow riffles in fast-flowing water (1) (3).

The southwestern arched-mouth nase has a relatively short lifespan, at up to four years. Both the male and female southwestern arched-mouth nase become sexually mature at around two years old, but the female usually matures at a larger body size than the male. This species may lay relatively large numbers of eggs, with the number produced correlating to the female’s body size. Females of 10 centimetres in length are generally estimated to produce around 3,999 eggs. The southwestern arched-mouth nase spawns between January and April (2) (3) (4).

Little other information is available on the biology of the southwestern arched-mouth nase, but, like other members of the Cyprinidae family, it is likely to feed on a range of animal and plant material. Members of this group lack teeth in the jaws, instead processing food using modified bones in the throat, known as ‘pharyngeal teeth’ (7).

The most significant threat to the southwestern arched-mouth nase is habitat loss due to drought, which is exacerbated by climate change and water extraction for human use (1) (2) (4) (8). The pools that this species survives in during the summer have a tiny total area, meaning that longer, more severe droughts would put the southwestern arched-mouth nase at greater risk of extinction (1) (8).

Further threats to the southwestern arched-mouth nase’s habitat come from dam construction and a reduction in water quality, due to pollution and sand extraction. Sand extraction can also destroy spawning areas. This species may also be affected by the introduction of non-native fish (1) (2) (4) (5) (9), and its populations have quite low genetic diversity, probably as a result of recent population declines (10).

The southwestern arched-mouth nase is listed as Critically Endangered in the Portuguese Red Book, and is covered by national and international legislation (5). Various sites at which it occurs have been designated as special areas of conservation, but still lack management measures for this species (5) (10).

As this species has only recently been described, little is known about its biology and habitat requirements, and there have not been any specific actions to conserve it. Further research into the southwestern arched-mouth nase is therefore needed, to better inform appropriate conservation measures (5).

The habitat of the southwestern arched-mouth nase also requires urgent protection, particularly the summer pools on which it depends. This species would benefit from habitat restoration, improvements to water quality, and measures to prevent water extraction during periods of drought (2) (4) (5), as well as the creation of new sheltered pools (4) (6). Some studies have already looked at the effects of habitat improvement schemes on the southwestern arched-mouth nase (11).

Further recommended conservation measures for this small endemic fish include controlling introduced species (2) (4) (5) and increasing public awareness about the conservation of aquatic habitats (5). To maintain and increase its genetic diversity, the southwestern arched-mouth nase also requires measures to reconnect its populations (5) (10). Scientists have recommended reintroducing this species into streams between Bensafrim and Arade, as well as maintaining it in artificial refuges (10).

Find out more about the southwestern arched-mouth nase and its conservation:

• FishBase - Iberochondrostoma almacai:
  http://www.fishbase.org/summary/SpeciesSummary.php?id=62346
• Livro Vermelho dos Vertebrados de Portugal - Chondrostoma almacai:
  http://portal.icnb.pt/NR/rdonlyres/CB478D55-FC7C-4EE2-AEFC-84B423307566/3101/LVVP_Peixes_Chondrostomaalmacai.pdf (In Portuguese)