The green terror (Aequidens rivulatus) is a colorful freshwater fish in the cichlid family. The fish originates from the Pacific side of South Americain the coastal waters from the Tumbes River in Peru to the Esmeraldas River in Ecuador. Males and females may reach lengths of 30 centimetres (12 in). Females are sexually mature at around 12 centimetres (4.7 in).
As the name implies, late-juvenile-phase and adult-phase specimens can be very aggressive. This is not guaranteed, however, and peaceful individuals can be observed. Juvenile green terrors are often sold in pet and aquarium stores for the aquarium hobby. This species is not to be confused with the blue acara cichlid, Andinoacara pulcher), which is similar in appearance; the Blue Acara is not as aggressive and does not grow as large as the Green Terror.
The fish is somewhat deep-bodied, possessing a prominent forehead. Adult males develop a pronounced forehead hump, composed of fatty tissue. Juveniles are tan colored with silver-blue flecks and lack the bright iridescent blue, green, and orange coloration and long, flowing fins of adult specimens.
In nature, Green terrors live in a tropical climate and prefer water with a 6.5–8.0 pH, a water hardness of 25.0 dGH, and a temperature range of 20–24 °C (68–75 °F)