The South European Toothcarp is a small, endemic fish of the Mediterranean Sea belonging to the family Cyprinodontidae. Its most prominent feature is the intense difference in appearance between the two sexes. The males are smaller and have bold, dark vertical stripes on a silver or light-blue background, while their fins are often yellow. The females are larger and have a simpler greyish colour with irregular dark spots on their sides instead of stripes. The body is short and thick with a mouth that points upwards for surface feeding.

It is the absolute master of difficult environments because it lives primarily in shallow coastal waters like lagoons, river estuaries, and salt pans. It is an extremely resilient species that can survive in conditions that would be fatal to other fish. It withstands massive fluctuations in temperature and salinity because it can live in nearly fresh water as well as in hypersaline water where salt begins to crystallise.

This is a very small fish. The length of the females reaches a maximum of six centimetres while the males remain even smaller and usually reach between four and five centimetres.

The species is omnivorous and feeds mainly on microscopic invertebrates. Its preferred food consists of mosquito larvae, which it hunts in shallow waters and among vegetation. In salt pans, it also feeds on small crustaceans such as brine shrimp, along with various algae and plant debris.

Breeding lasts throughout the summer and usually from April to September. The males become aggressive and claim a small territory to attract the females. The females lay a few eggs at a time, which stick to aquatic plants with the help of fine fibres.

The International Union for Conservation of Nature classifies the South European Toothcarp as a species of Least Concern, although local populations are declining. Scientific studies have highlighted that the greatest threat to the species is not pollution but competition with the invasive Mosquitofish, which was introduced for the same purpose of mosquito control. Research shows that the invasive species displaces the native toothcarp from fresh and brackish waters, but the native fish manages to survive and dominate in the highly saline waters of salt pans, where the invasive competitor cannot live.