Not strictly a freshwater fish, the Small-mouthed hardyhead grows to 6.5cm long. It was once very abundant in the lower reaches of both the Murray Darling Basin and Gulf streams. While it remains extant in both of these drainage regions, in both, it is now far less common. The Small-mouthed hardyhead feeds in eel-grass beds (Zostera sp.), primarily on crustaceans and insects.