Kosswigichthys asquamatus SÖZER, 1942

Hazar Toothcarp, Scaleless Killifish

Etymology

Kosswigichthys: named for Turkish zoologist and geneticist Curt Kosswig (1903-1982), who helped Sözer in his study of toothcarps, in combination with the Greek noun ichthys (Gr. ἰχθύς), meaning ‘fish’.

asquamatus: from the Greek a- (Gr. ἀ-), meaning ‘without’, and Latin squamatus, meaning ‘scaled’, in reference to this species’ near-total lack of body scales.

Classification

Order: Cyprinodontiformes Family: Aphaniidae

Distribution

Contrary to some of the available information this species is not found in Iran and is endemic to Lake Hazar in the eastern Taurus mountains, southeastern Anatolia, Turkey. The lake is located just to the south of the city of Elâzığ and measures around 22km by 7km. Seismic activity caused by the eastern Anatolian fault line which passes beneath it has resulted in many changes in the water level over time, and it is also famed as one of the principal sources of the great Tigris river.

A botched attempt to drill a drain for irrigation in the late 1980s caused a dramatic reduction in water volume and A. asquamatus was subsequently included on the IUCN Red List of Threatened Species for a couple of decades. The level of water has now been stablilised and the species appears to have recovered although given the highly restricted range it should never be considered totally secure especially given the continuing pollution and siltation of the lake. See the ‘notes’ section for a little more on the distribution of Aphanius in Anatolia.

Habitat

The water of the lake is rich in magnesium chloride with a hard, alkaline chemistry. This species has adapted to a more pelagic lifestyle than others in the genus and can be found swimming in schools outside the spawning season. During warmer months males form their breeding territories around algae-encrusted rocks.

Maximum Standard Length

35 – 40 mm.

Aquarium SizeTop ↑

A 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.

Maintenance

Even for long-term maintenance a simple set-up will suffice although certain aspects of water chemistry appear to be mandatory (see ‘water conditions’). The most important factors are the provision of cover and a suitable medium in which the fish can deposit eggs. Much of the available space can therefore be filled with acrylic wool mops (use a fine grade if available) and ideally filamentous algae.

Fine-leaved plants such as Java moss or Ceratophyllum can be used but may fail to thrive as the addition of marine salt to the water in the ratio of 1-2 g/L is necessary. Similarly, 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.

Water Conditions

Temperature: Active over a wide temperature range of 12 – 28 °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: The pH value in the lake ranges between 8.3 – 9.2 and we suggest aiming for similar values in aquaria. It will probably not survive under acidic conditions.

Hardness: 268 – 625 ppm. This species seems to require the presence of certain salts in order to ensure proper egg and fry development, with a combination of pure gypsum and epsom salts proving most successful at time of writing.

Diet

Aphanius species are essentially 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 ↑

Given its particular water requirements and precarious conservation status we strongly recommend maintaining it alone, the emphasis being on captive reproduction. Ideally it should be kept in a group with a ratio of two or three females to each male. Males are not as aggressive as those of most congenerics and several can usually be maintained together without problems especially outside the spawning season when this species tends to form schools.

Sexual Dimorphism

As with all members of the genus sexual dimorphism is pronounced. Males exhibit a body pattern consisting of 11-15 dark vertical bars with small dark spots on the head. The dorsal fin contains variable black and grey markings and there are two dark bars in the anal fin. When in spawning condition the overall body colour darkens to almost black. Females are larger and much plainer possessing only a series of variable dark blotches on the flanks and completely hyaline finnage.

Reproduction

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 very dark 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 of this subspecies are among the smallest among the genus and must be treated very 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 12-17 days and the tiny fry will require an infusoria–type food for several days until large enough to accept Artemia nauplii, microworm etc.

NotesTop ↑

This little-known, relict species possesses some unique morphological and behavioural traits when compared with its congeners and the genus Kosswigichthys was erected for it in the original description. It has a much more elongate body profile than other Aphanius spp., almost total absence of scalation on the body and three rows of conical (as opposed to tricuspid in all other species) teeth which set it apart. Work by Franz and Villwock in the 1970s revealed it to be a member of Aphanius and showed that individuals with conical teeth are found, albeit rarely, among populations of some other Turkish members of the genus.

The partially-scaled Anatolian lake district species are also well-documented by science (see below), and it appears that while such characteristics as tooth structure and scalation remain varied in other Aphanius they have become fixed in A. asquamatus due to a relatively high rate of molecular evolution. More recent phylogenetic studies have supported its placement within the genus, confirming it as sister species to a clade from western Anatolia that includes the A. anatoliae species group, A. danfordii and A. villwockii.

You’re unlikely to find this species on sale in aquatic stores 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.

The Anatolia region represents a centre of diversity with ten described species endemic to the region. These are thought to have diverged as a result of the splitting of what was originally a vast lake covering much of modern Anatolia. Two separate divergence events occured, the first resulting in the western separation of A. asquamatus, A. danfordii and A. villwocki around 12-15 million years ago (possibly earlier in the case of A. asquamatus). Lakes Tuz, EÄŸirdir and BeyÅŸehir are remnants of the central part of the lake where A. anatoliae now occurs and there exist three other species in the Turkish Lakes region that were isolated when the eastern end of the lake became disconnected around 11-12 mya.

They were further separated from one another 7-8 mya and have evolved independantly to survive in bitter lake environments containing high levels of alkaline carbonates and sulfates. Due to a historic lack of competition, predators and aquatic vegetation in their habitats they have developed distinctive limnetic (open water) characteristics including an elongated, relatively slim body shape and unique jaw morphology.

A. splendens, A. sureyanus and A. transgrediens also show differences in the extent of scalation on the body which is now known not to be a fixed characteristic and actually results from an unpredictable variation in their genes. It’s been hypothesised that this occured due to a lack of selective pressures allowing individuals with less scalation to survive and breed, thus facilitating an overall increase in scale variation. This may represent a case of regressive evolution as neither the stream/river dwelling populations of A. anatoliae or other Anatolian Aphanius (fully-scaled) nor A. asquamatus (completely scaleless) exhibit such variations.

The genus 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, inexplicably, listed as a species of Lebias by some sources although that 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.

References

1. Blanco, J. L. 2005 - SEI/GEVA Ficha.
   Aphanius asquamatus (Sözer, 1942).
2. Hrbek, T. and A. Meyer. 2003 - J. Evol. Biol. 16(1): 17-36.
   Closing of the Tethys Sea and the phylogeny of Eurasian killifishes (Cyprinodontiformes: Cyprinodontidae).
3. Hrbek, T., F. Küçük, T. Frickey,K. N. Stölting, R. H. Wildekamp and A. Meyer. 2002 - Mol. Phylogenet. Evol. 25(1): 125-137.
   Molecular phylogeny and historical biogeography of the Aphanius (Pisces, Cyprinodontiformes) species complex of central Anatolia, Turkey.
4. Wildekamp, R.H., F. Küçük, M. Ünlüsayin, and W. V. Neer. 1999 - Turk. J. Zool. 23: 23-44.
   Species and Subspecies of the Genus Aphanius Nardo 1897 (Pisces: Cyprinodontidae) in Turkey.