Few fish species. Represented by a small number of populations in a narrow range scattered over a large area.

These are species that are not directly threatened with extinction, but which may disappear rapidly because: a) they have very few individuals and/or populations; b) they occur in a very limited area and in specific locations.

A rare species is a group of organisms that are very unusual, rare or infrequent. This term can be applied to a plant or animal taxon and is different from the term 'endangered' or 'threatened with extinction'. 

The definition of a rare species may be made by an official body, such as a national government, state or province. 

The term is more commonly used without reference to specific criteria. 

Rare is when a particular species is represented by a small number of organisms worldwide, usually less than 10,000. However, a species with a very narrow endemic range or a fragmented habitat also affects the concept. Almost 75% of known species can be classified as 'rare'. 

Rare species are those with small populations. Many will move into the endangered or vulnerable category if the negative factors affecting them continue. This is particularly true in the world's oceans, where many "rare" species that have not been seen for decades may have died out unnoticed, if they are not already on the brink of extinction, such as the Mexican vaquita. 

A species can be endangered or vulnerable, but not considered rare, if it has a large, dispersed population. The IUCN uses the term 'rare' to refer to species that occur in isolated geographical locations. 

Rare species are generally considered to be endangered because, when populations are small, they are obviously less likely to recover from ecological disasters.For example: the Steller sea gudgeon (lat. Romanogobio albipinnatus) is a rare, poorly studied species of the carp family. It is found in the basins of the Baltic Sea (only the Vistula system), the Black Sea, the Caspian Sea and the Sea of Azov. It is absent from the Crimean and Kuban rivers. Two of the three subspecies occur in Russia: R. albipinnatus albipinnatus  in the Volga and Urals and R. albipinnatus belingi in the Dnieper basin. Possibly a separate subspecies in the Don. Non-target species, rare in some parts of its range. Listed in the Red Book.