Acheron spring goby

Knipowitschia milleri, the Acheron Spring goby, is a species of goby endemic to Greece where it can be found in nearly stagnant, clear, fresh to very slightly brackish waters with abundant weed growth.

Description
The largest recorded specimen was 2.6 cm SL, the oldest recorded specimen was two years old.

Distribution and ecology
It is restricted to the river Acheron delta in Greece. It is found in fresh and slightly brackish waters, often with abundant vegetation, and sand or mud substrates.