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Order: Cyprinodontiformes Family: Cyprinodontidae


Endemic to a small part of southern Spain, mostly within the lower Guadalquivir River basin and along the country’s southern Atlantic coastline with a single locality in the territory of Gibraltar. There remain only nine populations which are geographically isolated from one another, thus restricting natural genetic flow, around half of which are at risk of being wiped out by non-native, highly-competitive Gambusia holbrooki or Fundulus heteroclitus

It has been considered endangered by the IUCN since 2006 and captive breeding projects are underway but protection of its habitats remains woefully inadequate and repeated droughting in the region is not helping the situation. There have also been isolated incidents such as a mine spill in 1989 that released 5 million m³ of toxic mud and acidic water into the River Guadiamar and polluted 5-7000 ha of the Doxana National Park in the Guadalquivir delta. The IUCN survey concluded that its numbers may have declined by as much as 50% in the previous decade.


One population resides in a very shallow (30 cm average depth) freshwater lagoon with a silty clay substrate and poor growth of aquatic vegetation while another inhabits a freshwater stream but in all other cases this species occurs in small, hypersaline coastal channels. Marginal vegetation tends to grow poorly and Cladophora spp. algae are the most dominant submerged plants while substrates are composed of silt and clay.

In the hypersaline locations A. baeticus is usually the only fish species present and abundant but when it occurs alongside Gambusia, Fundulus or native, predatory species it can only be found in small numbers. Most of the habitats are also subject to seasonal drying with the fish surviving in tiny pools for several months of the year so the challenges facing this species are manifold.

Maximum Standard Length

35 – 50 mm.

Aquarium SizeTop ↑

pair or trio can be kept in a container with base dimensions of 60 cm x 30 cm or so but as a general rule members of this genus do better when maintained as a larger group in a space measuring upwards of 120 ∗ 30 cm.


Even for long-term maintenance a simple set-up will suffice. The most important factors are the provision of many broken lines of sight and a suitable medium in which the fish can deposit eggs. Female and subdominant male individuals must be offered the opportunity of respite from the aggressive alpha males during the spawning season so much of the available space can be filled with acrylic wool mops (use a fine grade if available), clumps of Java moss/other fine-leaved plant and ideally filamentous algae

There’s no need to add a substrate although inert sand or gravel can be added if you prefer, and filtration need not be too strong either. It is possible, and preferable, to maintain it outdoors all year round in many countries and it will show better colours and overall condition if exposed to at least a few hours of natural sunlight each day. Ideally you should know the population from where your fish originated as some will do best in freshwater but if in doubt we recommend the addition of marine salt in the ratio of 1-3 g/L.

Water Conditions

Temperature: Active over a wide temperature range of 2 – 30 °C. Artificial heating is not required in all but the coldest climates and it should be provided with a ‘winter’ period of several months during which it is maintained at low temperatures or it is likely to suffer both reduced fecundity and a shortened lifespan.

pH: 7.0 – 9.0. It will probably not survive under acidic conditions.

Hardness: 179 – 625 ppm


Aphanius species are basically micropredators feeding on small aquatic crustaceans, worms, insect larvae and other zooplankton although algae and other plant material is also taken at times. In the aquarium they will learn to accept dried foods in most cases but should also be offered regular meals of small live or frozen fare such as Artemia, Daphnia or bloodworm. This is particularly important during the months of spring and summer due to their high reproductive effort throughout this period. If the aquarium or container does not contain filamentous algae try to introduce a good quality dried product with added Spirulina content to the diet.

Behaviour and CompatibilityTop ↑

Its particular water requirements and aggressive spawning behaviour make A. baeticus a poor choice for the community aquarium. Given its precarious conservation status the emphasis should also be on captive reproduction and we strongly recommend maintaining it alone. It should be kept in a group with a ratio of two or three females to each male being the ideal.

Sexual Dimorphism

As with all members of the genus sexual dimorphism is pronounced. Males exhibit a series of 14-17 silvery vertical bars in the rear portion of the body with usually 4-5 darker bars in the caudal fin. The dorsal, ventral, anal and caudal fins are suffused with a light blue colouration with a dark distal band in the former three and 4 rows of dark spots extending into the latter two. Females are larger and much plainer possessing only a series of variable dark blotches on the flanks along with a roughly circular black marking on the caudal peduncle and completely hyaline finnage.


A. baeticus shows reproductive adaptations to unstable environments and fluctuating population sizes with a relatively short lifespan (<2 years in most cases), early sexual maturity (often within three months of age) and a high reproductive effort. Two generations are usually produced within a spawning season and a single female is capable of releasing up to 1000 eggs per year.

Captive reproduction is not difficult if the tank or container is properly arranged and maintained (see ‘tank set-up’). It is a fractional spawner with females depositing eggs on a more-or-less continuous basis between the months of April and September. Males form temporary territories which they defend against rivals while attempting to entice females to spawn. Dominant individuals will show more intense colouration. Eggs are released singly or in small batches and are attached to algae or other surfaces by means of small filaments. Aphanius typically eat their eggs/fry and the medium should therefore be checked on a daily basis during the spawning period.

The eggs are very small and must be treated carefully. Use a fine pair of forceps to gently remove pieces of medium with eggs attached whilst avoiding contact with the eggs themselves. Alternatively the entire medium can be removed and replaced every couple of days. The medium/eggs should be transferred to a container with water of the same chemistry and temperature as that of the adults. The incubation period can vary a little with the temperature but is usually between 7 -14 days with the fry being large enough to accept Artemia nauplii, microworm etc. immediately after they become free-swimming.

NotesTop ↑

Prior to its description this species was considered a geographic variant of A. iberus but the 2002 paper revealed the pair to be genetically quite distinct and also highlighted some morphological differences. It is distinguished from A. iberus by possessing 8-9 (usually 8) branched dorsal fin rays (vs. 8-9, sometimes 10), 9-11 branched anal fin rays (vs. 8-9), a deeper, more elongate body shape, noticeably shorter snout, relatively thick (vs. thin) vertical bars in males and a flank patterning consisting of a few large (vs. numerous, small) dark markings in females. The two species are thought to have diverged from one another around 5 million years ago, around the time of the opening of the Straits of Gibraltar.

You’re unlikely to find it on sale in aquatic stores as its collection and trade is currently prohibited although it may be available via specialist breeders or associations from time-to-time. While Aphanius are certainly not as colourful as some of their relatives their interesting behaviour and continuous activity make them fascinating aquarium subjects and well worth a try if you possess the dedication to take on a long-term maintenance project since conservation is key with all members of the genus.

It currently contains 22 species and subspecies which are thought to have derived from a common ancestor originally distributed around the periphery of the former Tethys Sea. None are particularly well-documented in aquarium literature although some are very beautiful and the majority are not too difficult to maintain and breed. Sadly most are on the verge of extinction for one reason or another with several existing only in remnant, highly-localised populations. 

In practically all cases the root cause for this decline is the activity of humans and although some species are now protected by conservation law the mismanagement and degradation of their habitats continues at an alarming rate. A few species are still sometimes listed as members of Lebias although that generic name has long been considered a synonym of Cyprinodon by most authorities and an ICZN committee voted to suppress the name in favour of Aphanius as recently as 2003.


  1. Doadrio, I., J. A. Carmona and C. Fernández-Delgado, 2002 - Folia Zoologica 51(1): 67–79
    Morphometric study of the Iberian Aphanius (Actinopterygii, Cyprinodontiformes), with description of a new species.
  2. Hrbek, T. and A. Meyer, 2003 - Journal of Evolutionary Biology 16(1): 17-36
    Closing of the Tethys Sea and the phylogeny of Eurasian killifishes (Cyprinodontiformes: Cyprinodontidae).
  3. Oliva-Paterna, F. J., I. Doadrio. and C. Fernández-Delgado, 2006 - Environmental Biology of Fishes 75(4): 415-417
    Threatened Fishes of the World: Aphanius baeticus (Doadrio, Carmona & Fernández Delgado, 2002) (Cyprinodontidae).

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