Taxonomy & naming
The species was first named by Neu in 1937 as Cyprinodon sureyanus, based on material from Lake Burdur in Burdur Province, southwestern Turkey. Eleven years later, working independently, the Turkish ichthyologist F. Akşiray described the same lake's population again in 1948 under the name Aphanius burduricus — a Latinised toponym referring directly to Lake Burdur. Under the rules of zoological nomenclature, the earlier name takes priority once the two are recognised as referring to the same species, and Eschmeyer's Catalog of Fishes (CAS) accordingly treats Aphanius burduricus Akşiray, 1948 as a junior synonym of the valid name. Following the genus-level revision that split the Anatolian lake-and-spring Aphanius into the resurrected genus Anatolichthys, the currently valid combination is Anatolichthys sureyanus (Neu, 1937).
Because Akşiray's name circulated widely in the Turkish and European ichthyological literature for decades before the priority issue was resolved, the species is still very often encountered under 'Aphanius burduricus' or 'Burdur killifish' in older field guides, hobbyist references, and even some conservation documents — including the CARES Fish Preservation Program priority list, which carries it under the still-older subspecies-style designation Aphanius anatoliae 'sureyanus'. All of these names refer to the same single population.
Anatolichthys and its immediate relatives belong to the family Aphaniidae, a clade of small Old World toothcarps distributed across the Mediterranean basin, the Middle East, and Central Asia. The Burdur killifish is one of the more morphologically and ecologically distinctive members of this group, owing to the extreme physicochemical regime of its sole habitat.
This fish was long listed as Aphanius burduricus; Eschmeyer's Catalog of Fishes gives priority to Neu's earlier name and places the species in Anatolichthys, and the current combination Anatolichthys sureyanus is followed here.
Morphology
The Burdur killifish is a small, compact toothcarp reaching a maximum of approximately 2 in standard length according to Seriously Fish, with FishBase recording a maximum total length of 2 in. Body form is typical of the genus: laterally compressed, with a somewhat rounded, blunt snout, an upturned mouth suited to surface and mid-water feeding, and a single dorsal fin set far back over the anal fin.
Sexual dichromatism is pronounced, as in most Anatolichthys and their Aphanius relatives. Males in breeding condition display a silvery to blue-grey ground colour overlaid with 10–15 irregular pale crossbars or blotches that give a striped or banded appearance; the fins may carry a yellowish tinge. Females are larger-bodied when gravid and cryptically coloured in mottled olive-brown tones with less distinct or absent patterning — an asymmetry that is the rule across the genus and reflects differing predation pressures on the sexes during the spawning season.
The teeth are small and multicuspid, adapted for picking up invertebrates and algae from surfaces — a fine-grained dietary tool well suited to the biofilm-rich shallow margins of alkaline lakes. Scales are moderately large and cycloid. There are no external features that meaningfully distinguish this species from other Anatolian Aphaniidae in the field; identification relies on geography (the species does not co-occur with any congener in Lake Burdur), measurements, and the distinctive water chemistry of the lake itself.
Habitat
Lake Burdur is a closed-basin tectonic lake in the Taurus Mountains of southwestern Turkey, sitting at approximately 2789 ft above sea level. It has no surface outlet; water loss is entirely through evaporation, which has concentrated dissolved minerals — primarily sodium sulfate and sodium chloride — to extraordinary levels. Seriously Fish records pH values ranging from 8.0 to 10.0, averaging around pH 9, with dissolved solids (hardness) of 268–625 ppm. The lake is effectively a soda lake, distinctly alkaline and mineralised, though not as extreme as African rift soda lakes such as Natron or Magadi.
Anatolichthys sureyanus occupies the entire lake, from the warm, shallow littoral margins where aquatic vegetation and filamentous algae provide cover and feeding substrate, to somewhat deeper open water. Water temperatures span a wide seasonal range — Seriously Fish gives 41–72 °F — reflecting the lake's continental montane climate, with cold winters and warm summers. The lake never freezes completely at the surface, and the fish persist through winter at low temperatures in a slowed metabolic state.
This species has no known satellite populations, relict populations in nearby springs, or metapopulation connectivity with other water bodies. Its entire global range is the lake itself, making it among the most geographically restricted fish on Earth.
Feeding
In nature Anatolichthys sureyanus is a micropredator and opportunistic omnivore. Seriously Fish records a diet comprising small crustaceans, aquatic worms, insect larvae, and zooplankton, supplemented by algae. This dietary profile is typical for Aphaniidae in saline or brackish environments, where macroinvertebrate diversity is reduced and biofilm and algal crusts on the lake bottom and rocks represent a consistent secondary food source.
The upturned mouth is adapted for taking prey at or near the water surface, and surface-film organisms — chironomid pupae, emerging insects — are likely important seasonally. In an alkaline closed-basin lake with few competing fish species, the Burdur killifish occupies the micropredator niche across the water column without significant competition from other vertebrates.
In captivity the species readily accepts live and frozen Artemia nauplii, Daphnia, bloodworm, and tubifex. Small pelleted foods are taken once the fish are settled. The diet should include an algae component; spirulina-enriched foods or the natural biofilm that grows on surfaces in a mature tank are beneficial. Feeding in hard, alkaline water that approximates the lake chemistry improves colour and vitality.
Mating
Anatolichthys sureyanus is a non-annual species — it lives in a permanent water body with no seasonal desiccation, and its reproductive strategy reflects this. Rather than burying diapausing eggs in substrate to survive a dry season, the fish is a fractional spawner that deposits small batches of adhesive eggs across an extended breeding season. Seriously Fish documents the breeding season as April through September, aligned with warmer water temperatures and longer photoperiods.
During this period males become territorial and competitive. A male courts a female through lateral displays and fin-spreading, positioning himself alongside her and nudging her toward a spawning site — typically algae, fine-leaved vegetation, or a hard substrate where eggs can adhere. The pair make brief, close-contact spawning passes in which eggs and sperm are released simultaneously. Eggs are shed singly or in very small batches and attach to the substrate via adhesive filaments, a delivery mode quite different from the massed egg-burial of annual killifish.
Males may mate with multiple females across the season, and their territorial behaviour — especially in the confined space of an aquarium — can lead to persistent harassment of females and subordinate males. Providing multiple females per male and sufficient visual barriers is essential in captivity to distribute male attention and allow females recovery time.
Breeding
Eggs deposited on algae or spawning substrate incubate directly in water with no diapause phase. Seriously Fish gives an incubation period of approximately 15–17 days at the water temperatures typical of the breeding season. The resulting larvae are small but more developed than annual-killifish hatchlings, reflecting the longer in-ovo developmental period. Fry become free-swimming shortly after hatching and can be reared on infusoria and freshly hatched Artemia nauplii.
In the aquarium, spawning is triggered or sustained by maintaining temperatures in the range of 64–72 °F, providing fine-leaved plants or synthetic spawning mops as egg-deposition sites, and keeping water alkaline and moderately hard in approximation of the natural lake chemistry. Eggs can be collected from mops and incubated separately in shallow containers of hard, alkaline water to protect them from predation by the adults. Checking mops every few days and transferring eggs to a separate rearing vessel prevents cannibalism.
Growth of fry is relatively steady at appropriate temperatures; juveniles can be raised on microfoods graduating to small live foods and crushed flake. Because the species is non-annual, it is comparatively long-lived for a killifish, and individuals in good conditions may reach several years of age — a meaningful contrast with annual species whose life expectancy is measured in months.
In the aquarium
The Burdur killifish is an uncommon species in the hobby, found mainly through specialist killifish societies and breeders rather than general aquarium shops — and it is still very often traded and discussed under the historical name Aphanius burduricus. Its exceptional water-chemistry requirements are the primary keeping challenge: the fish thrives in hard, alkaline conditions that many standard aquarium setups do not provide. A target pH of 8.0–9.5 with moderate to high hardness, achieved using sodium bicarbonate or specialist Rift Lake salts, approximates the natural environment and is essential for long-term health and breeding success. Very soft or acidic water causes rapid deterioration.
A species tank of 15–20 US gal or larger, decorated with fine-leaved plants tolerant of alkaline conditions (such as Vallisneria) and open swimming space over a sandy substrate, suits the fish well. Temperatures of 64–75 °F are appropriate, with a winter cool-down toward the lower end of that range mimicking the seasonal variation of Lake Burdur. Males are aggressive among themselves; a ratio of one male to two or more females reduces the intensity of male competition. The tank must be well covered, as Aphaniidae are capable jumpers.
Keeping and breeding this species carries real conservation significance. Wild populations face ongoing pressure from lake-level decline, and captive-breeding programmes — however modest in scale — maintain a genetic resource outside the single precarious natural population. Hobbyists keeping the fish are encouraged to connect with killifish societies that coordinate strain management and maintain studbook records for threatened toothcarps.
Conservation
The IUCN Red List assesses Anatolichthys sureyanus as Endangered, based on a reassessment by Freyhof (2014). The species meets Endangered criteria under criterion A2e (population size reduction inferred from decline in area of occupancy, extent of occurrence, and/or quality of habitat). Because the entire global population is confined to a single lake, any threat to that lake is a direct existential threat to the species.
The species also carries a CARES Fish Preservation Program priority listing — recorded there under the historical, subspecies-style designation Aphanius anatoliae 'sureyanus' and classified Endangered (CEN) — placing it firmly among the conservation-priority springs and lake fishes the hobby is asked to help maintain as an insurance population.
Lake Burdur has been shrinking. The lake lost approximately 70% of its surface area during the twentieth century due to agricultural water diversion — irrigation channels drawing from the rivers that feed the lake have cut inflow drastically, and the closed basin's water balance, entirely dependent on inflow exceeding evaporation, has tipped negative. As the lake shrinks, dissolved minerals concentrate further, and the shallow littoral zone — the most productive habitat for the fish — recedes. Introduced species pose an additional threat: the mosquitofish (Gambusia holbrooki), released widely across Turkey as a mosquito-control measure, has established in many Anatolian freshwaters and is a documented driver of killifish declines through predation on fry and direct competition.
The Burdur killifish is protected under Turkish national legislation, and the lake itself is designated a Ramsar Wetland of International Importance and a Special Protection Area, partly in recognition of its importance for wintering waterbirds. These designations have provided some degree of political attention but have not reversed the hydrological decline. A combination of reduced agricultural abstraction, enforcement of water-management agreements, and active monitoring of fish population size would be required to improve the species' prospects. Given that it has no alternative habitat anywhere on Earth, the margin for error is extremely narrow.