Green terror

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: destroys most plants.

Feeding

Carnivore-leaning omnivore. Cichlid pellets (large, high-protein) form the staple diet. Supplement with frozen prawns, frozen mysis, frozen bloodworm (for juveniles), live earthworms, and live feeder shrimp. Larger adults take whole market shrimp, mussel, and fish fillet. Blanched peas and spinach provide fiber. Feed once or twice daily for adults. Juveniles benefit from 2-3 smaller feedings. The green and blue body coloration intensifies on a varied diet with carotenoid-rich foods (shrimp, krill, astaxanthin-enhanced pellets). Avoid feeder fish as a routine food source; they carry disease and parasites and provide poor nutrition compared to prepared foods.

Compatibility

• Genuinely aggressive. The common name is not marketing hyperbole. Males become increasingly territorial as they mature and will dominate a tank of 300 L if not matched with equally assertive tankmates.
• Not a community fish in any conventional sense. Tankmates need to be large, robust, and able to hold their own: other large South American cichlids (oscars, severums, geophagus), large catfish (pleco species, synodontis), and large loaches. Anything small enough to fit in the mouth is food.
• Breeding pairs are significantly more aggressive than single specimens. A male-female pair defending eggs or fry will attack everything in the tank, including fish twice their size. Dedicated species tanks are the safest option for a breeding pair.
• Males reach 25–30 cm and develop a pronounced nuchal hump (forehead bump) with age. Females stay smaller at 15–20 cm. The size difference and the hump make sexing adults relatively easy.

Origin and habitat

Native to the Pacific side of South America. A. rivulatus occurs from the Tumbes River in far northern Peru to the Esmeraldas River drainage in Ecuador. The range covers the Guayas, Santa Rosa, Zarumilla, and Tumbes basins. Replaced by A. blombergi in the Esmeraldas basin and A. stalsbergi south of Tumbes in Peru from Piura to Ica. Described by Günther in 1860 as Chromis rivulata. A major identity confusion exists: A. stalsbergi (described as separate in 2009 by Musilová, Schindler, and Staeck) is "often considered the 'true' green terror". HandWiki distinguishes them: A. stalsbergi has "scales with light centres and dark edges, and narrow clearly defined white fin edging," while A. rivulatus has the "reversed" scale pattern with gold-orange or less defined white fin edges. A. rivulatus is polymorphic and can display either fin color. Males reach around 20 cm; females smaller at up to 12 cm. Males develop a nuchal hump; these only develop during breeding season in nature, but in aquaria many specimens possess enormous, permanent humps. Males often kill females if paired incorrectly; buying 6+ juveniles and letting pairs form naturally is the safer route.

Breeding

Substrate spawner. A pair cleans a flat rock or digs a pit in the sand and the female deposits 200-600 eggs. Both parents guard the clutch fiercely. Aggression toward tankmates reaches its maximum during this period. Eggs hatch in 3-4 days. Fry become free-swimming 4-5 days later and are herded around the tank by both parents. Parental care is extended, lasting 4-8 weeks, sometimes longer if the pair doesn't re-spawn. Fry eat baby brine shrimp and finely crushed pellet from day one. Growth is fast with good feeding. Breeding is not difficult in a dedicated pair tank with a flat stone and stable water conditions. The challenge is the aggression: a breeding pair in a community tank will cause serious damage to tankmates. Pairs bond strongly and may remain together for years, spawning repeatedly. Production per brood is high enough that rehoming or selling juveniles becomes necessary quickly.

Common problems

Aggression management is the primary keeping challenge. A single green terror in a large community with other robust cichlids is manageable. A breeding pair requires planning, space, and an understanding that everything else in the tank will be subordinate. Hole-in-the-head disease (Hexamita) affects green terrors more than many other cichlids, typically manifesting as pits along the lateral line and on the head. The cause is multifactorial: poor water quality, vitamin/mineral deficiency, and chronic stress all contribute. Treatment with metronidazole is effective if caught early. Prevention is a clean tank, varied diet with vegetable matter, and minimal chronic stress. Lateral line erosion (HLLE) overlaps with Hexamita and may have similar causes. Ich in newly acquired fish is treated with standard methods; the species tolerates medication well. Tank size is frequently underestimated; adults need 300 L for a single specimen and 400+ for a pair.

Bioload

Further reading

• Stocking ideas by tank size