Aphanius transgrediens (ERMIN, 1946)

Classification

Order: Cyprinodontiformes Family: Cyprinodontidae

Distribution

Endemic to the Lake Aci (often spelled “Aci”) basin in the Turkish Lakes (Göller Bölgesi) region of the west Taurus mountains, southwestern Anatolia, Turkey where it has been considered critically endangered by the IUCN since 1996. See the ‘notes’ section for a little more on the distribution of Aphanius in Anatolia.

Habitat

The lake is called “Acigöl” in Turkish which literally translates as “bitter lake” and is so-named because of the important reserves of sodium sulfate and other salts it contains. The surface area can vary between 100 km² and 35 km² depending on the time of year with exposed salt flats being intensively harvested for commercial purposes. It is mostly fed by sulfurous springs along its southeastern edge but also has a hydraulic relationship with magnesium-rich underground aquifiers.

Due to the extreme chemistry and fluctuation in water levels the fish are rarely found in the lake itself and are mostly restricted to a handful of fresh and slightly brackish water springs around its margins. These are typically very shallow with growths of filamentous algae and an unidentified Chara species. During winter months particularly high periods of rainfall sometimes allow the fish to move around the periphery of the lake into adjacent inlets so there used to exist a degree of genetic flow between populations.

During a 30-year study between 1930-1974 A. transgrediens could be found inhabiting 16 springs around the lake but during surveys conducted by a Spanish team in 2005 it was observed in just two of these and in 2008 only a single population remained; its extinction would appear to be inevitable. In the rest of its previous habitats it has been outcompeted by non-native mosquitofish, Gambusia affinis, which were introduced some time in the early 1990s and are spreading rapidly as they too move around the margins of the lake when the water level is high enough. Degradation of habitats has also played a part as the land is extensively used for grazing sheep and cattle.

Maximum Standard Length

45 – 50 mm.

Aquarium SizeTop ↑

A pair or trio can be kept in something around 24″ x 12″ x 12″/60cm x 30cm x 30cm/57 litres in size but as a general rule members of this genus do better when maintained as a larger group in a tank measuring upwards of 48″ x 12″ x 12″/120cm x 30cm x 30cm/113 litres.

Maintenance

Even for long-term maintenance a simple set-up will suffice. 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 is 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 35 – 86°F/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: 8 – 10. It will probably not survive under acidic conditions.

Hardness: 15 – 30°H

Diet

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 ↑

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.

Sexual Dimorphism

As with all members of the genus sexual dimorphism is pronounced. Males exhibit a body pattern consisting of 8-11 irregular, dark grey to black vertical bars with usually one or more dark bars in the otherwise colourless caudal fin. The anal fin and dorsal fins have a grey base but are mostly dark-coloured. 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 two separate peaks of activity at the onset of spring and end of summer. 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 6 -12 days and the tiny fry will require an infusoria–type food for several days until large enough to accept Artemia nauplii, microworm etc.

NotesTop ↑

The modified lower jaw and reduced scalation exhibited by this little-known species have seen it placed in the disused genera Anatolichthys and Turkichthys in the past and it is still sometimes listed as a species 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.

You’re extremely unlikely to find it 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 endemic species described to date. 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, Eğirdir and Beyşehir are remnants of the central part of the lake where A. transgrediens now occurs and there exist three other locally endemic 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 an historic lack of competition, predators and aquatic vegetation in their habitats they’ve developed distinctive limnetic (open water) characteristics including an elongated, relatively slim body shape and unique jaw morphology.

A. anatoliae is the most easily distinguished of this A. anatoliae species complex as it’s the only fully-scaled member of the group – A. splendens, A. sureyanus and A. transgrediens all 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 the very isolated A. asquamatus (completely scaleless) exhibit such variations. The relatively wide genetic variation among the isolated populations when compared with the riverine ones suggests that genetic flow is an important factor in the structure of Aphanius populations (Hrnek et al., 2002).

As mentioned above the occasional movement of some A. transgrediens populations into neighbouring streams allows for a limited amount of genetic flow and this is reflected in its intermediate placing between A. anatoliae and A. splendens/sureyanus in terms of morphology – it exhibits an overall more uniform pattern of scalation, more-compact body form and less-angular jaw structure than the latter two.

The lake district species can also interbreed freely in aquaria and appear to form a distinct clade whereas the forms found in western and central Anatolia have been shown to exhibit differing degrees of sterility to the lake fishes. When this is considered problems with nomenclature arise and Villwock (2004) theorised that all subpopulations should be regarded as “species in statu nascendi” i.e. in the process of creation and referred to as A. anatoliae ssp. pending further study. Hrnek et al. (2002) alternatively suggested that the different clades may represent new species but agreed that further study is required. We’ve chosen to list them separately in order to avoid using sub-specific names.

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.

References

1. Bardakci, F., N. Tatar and T. Hrbek, 2004 - Biologia, Bratislava 59(5): 559—566
   Genetic relationships between Anatolian species and subspecies of Aphanius Nardo, 1827 (Pisces, Cyprinodontiformes) based on RAPD markers.
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. Hrbek, T., F. Küçük, T. Frickey,K. N. Stölting, R. H. Wildekamp and A. Meyer, 2002 - Molecular Phylogenetics and Evolution25(1): 125-137
   Molecular phylogeny and historical biogeography of the Aphanius (Pisces, Cyprinodontiformes) species complex of central Anatolia, Turkey.
4. Hrbek, T., K. N. Stölting, F. Bardakci, F. Küçük, R. H. Wildekamp, and A. Meyer, 2004 - Molecular Phylogenetics and Evolution 32: 297–308.
   Plate tectonics and biogeographical patterns of the Pseudophoxinus (Pisces: Cypriniformes) species complex of central Anatolia, Turkey.
5. Schulz-Mirbach, T. and B. Reichenbacher, 2008 - Geodiversitas 30(3): 577-592
   Fossil Aphanius (Teleostei, Cyprinodontiformes) from southwestern Anatolia (Turkey): a contribution to the evolutionary history of a hotspot of freshwater biodiversity.
6. Wildekamp, R.H., F. Küçük, M. Ünlüsayin, and W. V. Neer, 1999 - Turkish Journal of Zoology 23: 23-44
   Species and Subspecies of the Genus Aphanius Nardo 1897 (Pisces: Cyprinodontidae) in Turkey.
7. Zapater, M. 2005 - SEI/GEVA Ficha.
   Aphanius anatoliae transgrediens (Ermin, 1946).