Anatolichthys irregularis (Yogurtcuoglu & Freyhof, 2018)

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 707-708

Anatolichthys irregularis

Common name. Kaklık killifish.

Diagnosis. Distinguished from other species of Anatolichthys by: ● male with irregularly set and shaped, dark-brown bars, bars with white spots or vermiculate pattern, some large individuals plain, dark-grey with some yellow blotches / ○ male with yellow or white anal with narrow black margin / ○ female with numerous black, irregularly shaped stripes and vermiculate blotches on flank organised in midlateral rows / ○ body completely covered with overlapping scales. Size up to about 52 mm SL.

Distribution. Türkiye: Spring near Kaklık in Büyük Menderes drainage.

Habitat. Springs with dense vegetation and associated streams.

Biology. Live up to 3 years; biology as described in genus section.

Conservation status. CR; known only from a very small spring area, vulnerable to climate change, recreational activities, non-native species and desiccation.

Remarks. Anatolichthys irregularis is very closely related to A. maeandricus , but the colour pattern of male and

female can easily distinguish both species. It is likely that A. irregularis was recently isolated and has adapted to the gypsum springs where it lives.

Further reading. Yoğurtçuoğlu & Freyhof 2018 (description).

Spots or bars? Or even more open questions for Kaklık killifish. The colour patterns of fish have long fascinated evolutionary biologists due to their striking diversity and how they are influenced by sexual and environmental selection. Much of the data on the cellular and developmental mechanisms underlying colour-pattern formation, such as stripes, spots, or regular and irregular colour patterns, comes from zebrafish ( Danio rerio ). However, there is still much to be discovered about how these mechanisms are linked to the behaviour, ecology, and natural selection in the wild. Several cases, including recently evolved groups such as East African cichlids, have provided insights into the evolution of pigment patterns and triggered various hypotheses for testing. Anatolichthys irregularis is a young species worthy of future attention in this respect. It is unique in that its irregularly set and shaped spots and bars in the male (vs. regular bars in other Anatolichthys ). It was initially assumed that this significant difference in colour pattern, the dissociation of regular bars into an irregular and spotted pattern, must have been merely a phenotypic plasticity response to its extreme habitat (high sulfur concentration, high temperature, and oxygen-poor conditions). However, captive generations bred under different conditions have proven the colour patterns stable, as other Anatolichthys have demonstrated. Consequently, several open hypotheses have been formulated, including the evolution of isolated peripheral populations under strong selection and genetic drift due to limited population size. This phenomenon has already been demonstrated in zebrafish, where a change in pattern may be driven by a single mutation in a single gene, which is prone to selection through pleiotropic effects. Further reading. Parichy 2003, Gante 2018 (stripe evolution).

Anatolichthys maeandricus ; Işıklı spring, Türkiye; female, 40 mm SL. Anatolichthys maeandricus ; Işıklı spring, Türkiye; male, 30 mm SL.