Farsi toothcarp

The Farsi toothcarp (Esmaeilius persicus) is a species of pupfish belonging to the family Aphaniidae. It is endemic to the Maharloo Lake Basin in Iran, residing in springs, lagoons, and marshes containing fresh to brackish water.

Taxonomy
The species name, persicus, refers to Persia, the ancient name of Iran, where the fish is found. It was originally described as Cyprinodon persicus, later Aphanius. Then, in late 2011, a Late Miocene fossil genus Brachylebias was synonymised with Aphanius, which suggested a change to the extant species as there was a B. persicus which preoccupied the name. The replacement name proposed was farsicus, referring to the Fars Province, but this was not universally accepted. Finally, in 2020 it was added to a new genus Esmaeilius as Esmaeilius persicus.

Description
Farsi toothcarp reach approximately 4.9 cm in length. Like all members of its genus, the fish show sexual dimorphism. Females have numerous alternating light and dark bars, which gradually merge with the pigmentation on the rest of their bodies. The caudal fin spot has been recorded to be elongate, oval, or teardrop-shaped, but is almost always in the form of a lozenge.

Males, on the other hand, are similar in coloring to Esmaeilius sophiae, bearing light flank bars narrower than the alternating dark bars. The dorsal, anal, and caudal fins all have clear margins, whereas the rest of the fins are dark.