Portuguese arched-mouth nase  (Iberochondrostoma lusitanicum)

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

Endemic to parts of Portugal, the Portuguese arched-mouth nase (Iberochondrostoma lusitanicum) is a small, slender freshwater fish with a relatively small head and a downturned, arched mouth (2) (3) (4).

The dorsal fin and anal fin of the Portuguese arched-mouth nase are similar in size (2) (3) (4) and both have a slightly convex edge. The dorsal fin is positioned above or slightly behind the pelvic fins, and the tail fin has two rounded lobes (2) (3). There is a conspicuous lateral line along the side of the body (2).

In 2005, the Portuguese arched-mouth nase was separated from the closely related southwestern arched-mouth nase, Iberochondrostoma almacai, which has a smaller head, relatively longer snout and larger eyes. The two species also differ in details of their scales, gills and pharyngeal teeth (modified bones in the throat, used to process food) (2).

The Portuguese arched-mouth nase is restricted to a small area of west-central Portugal. It is found mainly in the western tributaries of the Tejo River drainage, in the Sado drainage, and in other small river basins including the Samarra, Colares and Ossos (1) (2) (3) (5).

This species usually inhabits small streams, with low or medium currents and with vegetation along the banks (1) (5) (6) (7). The Portuguese arched-mouth nase may survive the drier summer months in small pools, under the shade of vegetation (5).

The Portuguese arched-mouth nase breeds between January and May, when it groups together in spawning aggregations (3) (4) (5) (8) (9). These aggregations may involve large numbers of individuals, but courtship behaviour and spawning usually take place between one female and one or a few males (3) (8). The eggs of the Portuguese arched-mouth nase are adhesive, and stick to stones, gravel and vegetation (5) (8).

The lifespan of the Portuguese arched-mouth nase is around four years (4) (9). Individuals reach maturity at about two years old, although females may mature at a slightly larger body size than males. A female Portuguese arched-mouth nase of about 10 centimetres in length is estimated to produce around 3,999 eggs (9).

There is no information available on the diet of the Portuguese arched-mouth nase (7). However, like other members of the Cyprinidae family it is likely to feed on a range of animal and plant matter. Members of the Cyprinidae lack teeth in the jaws, instead using modified bones in the throat, known as ‘pharyngeal teeth’, to process food (10).

The Portuguese arched-mouth nase occupies a restricted range and its populations are highly fragmented, increasing its vulnerability to local extinctions (1) (5) (6) (7). Overall, this species has undergone a population decline of over 80 percent in the past decade (1) (6) (7), mainly due to the loss and degradation of its habitat (1) (5) (6) (7).

The freshwater streams inhabited by the Portuguese arched-mouth nase face a range of threats, including water extraction for agriculture and other human uses, infrastructure such as dams, and aggregate extraction (the extraction of crushed rock or gravel), which can affect water quality and destroy spawning areas. Water quality is also affected by pollution and by the destruction of riverside vegetation (1) (5) (6) (7) (11). Drought presents another serious threat, and may become worse in future with the effects of climate change (1).

The Portuguese arched-mouth nase is also likely to be affected by introduced fish species, which may act as predators or as competitors for food or other resources, or which may spread disease (1) (6) (7) (11).

The Portuguese Red Book lists the Portuguese arched-mouth nase as Critically Endangered (6). This species is covered by national and international conservation legislation (6), including the Bern Convention (12) and EU Habitats Directive (13). However, although various sites have been listed under the Habitats Directive, they still need management and planning measures directed at the Portuguese arched-mouth nase (6).

There are no specific conservation measures currently focusing on this endemic freshwater fish (5). Recommended actions include protecting and restoring its habitat, including maintaining minimum water levels during the dry season, and minimising the impacts of dam construction, water harvesting and aggregate extraction (5) (6) (7). Non-native species introductions also need to be controlled (6) (7).

Although the genetics and reproductive behaviour of the Portuguese arched-mouth nase have been studied, further research is needed into other aspects of its biology. It would also benefit from population monitoring and from the development of a species action plan (6) (7). The Portuguese arched-mouth nase has been shown to breed successfully in captivity, suggesting that captive breeding programmes could be a potential conservation tool for this species (5) (7) (8).

Genetic studies have suggested that populations of the Portuguese arched-mouth nase from the Tejo River and adjacent streams are distinct from those in the Sado basin. Further investigations may be needed to determine whether they are separate species (5).

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

• FishBase - Iberochondrostoma lusitanicum:
  http://fishbase.org.cn/summary/SpeciesSummary.php?genusname=Iberochondrostoma&speciesname=lusitanicum
• Livro Vermelho dos Vertebrados de Portugal - Chondrostoma lusitanicum:
  http://portal.icnb.pt/NR/rdonlyres/CB478D55-FC7C-4EE2-AEFC-84B423307566/3109/LVVP_Peixes_Chondrostomalusitanicum.pdf (In Portuguese)