Kosswigichthys, Sözer, 1942

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 745-746

Kosswigichthys

The only species in this genus is a highly specialised pelagic killifish endemic to a single ancient lake in Eastern Anatolia. Kosswigichthys is related to Anatolichthys , but both genera are long and well-separated. Kosswigichthys is one of West Asia’s few phylogenetically isolated and highly adapted lacustrine fish species. Its only

habitat, Lake Hazar, is a rift lake situated at the border of the Anatolian and Arabian plates within the East Anatolian Fault Zone ( EAFZ). This is one of the most significant active continental transform fault zones globally. Lake Hazar may be the oldest lake in West Asia, having possibly commenced development in the late Miocene or early Pliocene. However, some studies suggest a quite recent age for the lake, of about 150–180,000 years. Molecular data demonstrate that Kosswigichthys is isolated from Anatolichthys for longer than the late Miocene and that its ancestors may have inhabited the area much longer. It is possible that they found refuge in Lake Hazar, adapting to lacustrine conditions when the lake was formed. Their adaptations to lacustrine environments are similar to those of Anatolichthys saldae and A. splendens , which also show a lack of or reduced scales, a slender body, and a strongly upturned mouth. However, these species inhabit relatively young lakes and might have separated from their riverine ancestors only during the late Pleistocene. At present, K. asquamatus is the sole representative of the Aphaniidae in the upper Mesopotamian drainage system. Further reading. Freyhof & Yoğurtçuoğlu 2020 (generic structure of Aphaniidae ).

Kosswigichthys asquamatus ; Hazar Lake, Türkiye; female, ~ 33 mm SL. Kosswigichthys asquamatus ; Hazar Lake, Türkiye; male, ~ 30 mm SL.