Cyprinodon alvarezi

Cyprinodon: from the Ancient Greek κυπρῖνος (kuprinos), meaning 'carp', and ὀδούς (odous), meaning 'tooth'.

alvarezi: named for José Alvarez del Villar, friend of the author who collected this species in 1952 and handed over the task of describing it after initially intending to do it himself.

Originally endemic to a single isolated spring near the settlement of El Potosí in Nuevo León state, northern Mexico but has been extinct in nature since the late 1990s.

The type locality originally consisted of a single spring-fed pond located in an endorheic basin known as 'La Hediondilla' at the foot of the 'Cerro Potosí' mountain and around 1880 m AMSL.

It had been modified to make it larger via an earth and rock dam, and below the pond were several distributaries running for a distance of 1-1.5 km.

The water was very clear with abundant vegetation including species of Ceratophyllum, Najas, Nasturtium and Utricularia.

The pond was also home to another endemic pupfish, Megupsilon aporus, and an endemic crayfish, Cambarellus alvarezi, but is now completely dessicated with the water having been exploited for irrigation and other human uses.

Goldfish, Carassius auratus, were introduced to the pond sometime before 1961 and largemouth bass, Micropterus salmoides, were first recorded in 1974 alongside a corresponding decline in cyprinodontid populations.

Between 1983 and 1984 the water level dropped 1.5 m and by 1985 the pond had disappeared with only a trickle of water remaining in the distributaries. Slight recovery was observed during the early 1990s but only negligible populations of the endemic species were supported and by 1996 the water had gone.

An aquarium with base dimensions of 60 ∗ 30 cm24 ∗ 12 in or equivalent is just about acceptable for a single pair but like most members of the family Cyprinodontidae this species does best when maintained as a group in a larger tank or container.

Need not be too complicated so long as there are plenty of broken lines-of-sight.

Provide plenty of cover in the form of aquatic plants, wool mops, etc., and if using filtration air-powered, sponge-type units are best as these will not harm eggs or fry.

Lighting is unimportant but can be used if you wish, and growth of filamentous algae should be encouraged if possible.

Best-maintained alone, especially if the intention is for the fish to breed, but can be maintained in a well-researched community provided sufficient space is available.

Individual males require space to form territories but in most cases two or more can be kept in the same aquarium.

This species now exists only in captivity and its preservation is imperative meaning it is not recommended for the community fish keeper.