Aequidens rivulatus is a diurnal, South American cichlid sometimes said to possess two “faces” — striking beauty and beastly behavior. Often described as temperamental and boorish, one might wonder why anyone would keep such an awful fish. But the attractive side of its face far outweighs the horrid reputation, which is largely undeserved. This misunderstood fish truly emerges as a gem once the cloak of misunderstanding is peeled away.
Green Terror Looks
Aequidens rivulatus (pronounced a-key-dens-riv-you-lay-tes) is a freshwater, South American river cichlid. The male’s olive-green body displays speckled, blue-green iridescence, while the dorsal and caudal fins are capped with an orange or pink coloration. The pectoral fins are orange or yellow colored. Depending upon the lighting, some specimens appear to have a slight turquoise hue. A mature male, identified by a nuchal hump, can reach 10 to 12 inches in length. Hobbyists report captive-bred and raised male specimens reaching a length of more than 13 inches.
Female A. rivulatus sport the same colors as the male but are significantly subdued. The female often looks olive drab until bright illumination reveals her striking coloration. Females are smaller than the male, and reach 6 to 7 inches in length. Both sexes have a distinctive, mid-body black spot resembling the markings found on the American flagfish (Jordanella floridae). A life span of 10 or more years is common. There is much disagreement regarding slight variations in coloration of imported A. rivulatus. Some experts claim these fish are a different species while others say they are simply a variety.
The Green Terror is Misunderstood
The “green terror” moniker attached to A. rivulatus is somewhat unfair and probably originated with an inexperienced hobbyist housing these fish with slower, docile tankmates. This is a cichlid and that should raise a red flag, as I’ll explain below. Unfortunately, some retailers and fish traders do not warn their customers. This is how some fish get an unfair reputation for aggressiveness when, in reality, the fish is responding to cruel treatment.
These are actually quite peaceful fish that will bring years of happiness to those who understand and provide for their specific needs. Knowing this, hobbyists can prepare for the genial adolescent A. rivulatus that suddenly transitions into a beast upon reaching maturity and entering the breeding cycle. These fish are best housed with their own, like-sized kind.
A. rivulatus is monogamous and mated pairs should be housed alone in large aquariums. Placing tankmates with them is a gamble and potentially inhumane. Some aquarists report success keeping mature A. rivulatus with other species such as the Jack Dempsey (Rocio octofasciata) or Oscar (Astronotus ocellatus). I do not share that success with keeping cichlids, and have found smaller species like the A. rivulatus capable of pestering and even bullying larger tankmates.
Aequidens rivulatus Geographical Location
This fish is found primarily in the Rio Tumbes, Peru and the Rio Esmeraldas, Ecuador. Perhaps the iridescent blue-green color of A. rivulatus contributed to the naming of the clear, greenish waters of the Rio Esmeraldas. This is not a protected species nor is it reported to be a game fish. Collectors report finding A. rivulatus distributed throughout both rivers. Adults are primarily found in the deeper waters, while juveniles tend to reside in the shallow and backwater areas. Both rivers contain an eclectic substrate consisting of gravel, sand, mud, large river stones and thick beds of dead leaves. Water temperatures range from 69 to 79 degrees Fahrenheit depending upon elevation, time of year (rainy versus dry season) and water depth. They are found in water with velocity ranging from nearly still to rapid. The water pH ranges between 7.0 and 8.4 depending upon the collection region.
Keeping Aequidens rivulatus In Captivity
Begin planning your tank by meeting the green terror’s needs for plenty of open swimming space and lots of rocks to create shelters and territories. Be sure the rocks are stable, because these fish are active diggers and unsteady rocks can fall and crack the tank. Gravel substrate should be 1 or 2 inches deep.
Submerged live plants can be used, but select those with tough leaves like the Anubias. Attach your Anubias to a log using strong cotton thread. Plastic plants like Amazon Swords and Vallisneria provide nice color and “bullet-proof” decorations.
A. rivulatus needs impeccable water quality, which you can accomplish by frequent partial water changes and substantial filtration. The best water temperature for this species is about 72 degrees Fahrenheit. These fish are not in the “tank-busting” category, but they can certainly destroy many aquarium heaters. A canister filter will not only provide nice cross-tank water flow but also allow heating to be external to the tank.
Lighting for the aquarium is strictly a personal preference because the Anubias will grow in conditions ranging from very low to bright lighting. Higher lighting will cause algae to develop on the Anubias and rocks, but an electric timer can help control algae by limiting tank illumination to when you are home and available to enjoy the aquarium.
A. rivulatus has a voracious appetite. It is omnivorous, with a distinct preference for meat. Provide a balanced diet of live, frozen and flake or cichlid pellet foods. Recommended frozen foods include bloodworms, Mysis shrimp, krill and large (adult) frozen brine shrimp. Live foods include small worms, house flies and crustaceans.
Some erroneous information is circulating that these fish are voracious plant eaters. Like many cichlids, A. rivulatus uproot plants while digging in the substrate and some softer leaved plants could be shredded while this fish displays its boisterous behavior.
Green Terror Breeding Tips
A. rivulatus is a nest-guarding egg-layer. Breeding must be conducted in a dedicated tank. It is during breeding and nest guarding that this species is extraordinarily aggressive toward any other fish.
One challenge hobbyists’ encounter is obtaining pure breeding stock. Many cross-bred (hybrid) specimens are sold as A. rivulatus. An example of this is the breeding of two very similar looking species, A. rivulatus and A. pulcher. The only surefire way to obtain true A. rivulatus is to purchase from reliable breeders or have your local fish store special order them from a trusted wholesaler.
A. rivulatus are commonly reported to be substrate-breeders but if offered a choice, will readily lay their eggs on a piece of slate. Expect about 300 to 400 eggs that will hatch in about two to three days depending upon water temperature. Both parents will deposit the newborn fry into substrate pits and protect the nest. The fry are moved several times and become free swimming in about five days. Brood care lasts several weeks. These are very prolific fish, so have placement ready for the offspring prior to breeding. Fish stores can only take so many.
Ten Tips for Success with Aequidens rivulatus aka The Green Terror
1. Keep in a species tank if possible.
2. Make sure all tankmates are similarly sized and of the same temperament.
3. Under the right conditions, this fish is the proverbial aggressive cichlid, so keep it with like-kind or very large fish immune to bullying by a smaller tankmate.
4. Provide a very rocky, cichlid-type habitat preferably with swim-through caves and abundant hiding places.
5. Avoid overcrowding by providing at least 100 gallons for a pair of adult fish.
6. If aquatic vegetation is desired, use plastic or live plants with well-established root systems. A thick-leaved plant like Anubias that is firmly affixed to a log is ideal.
7. Feed a well-balanced diet of frozen foods like bloodworms, plankton, flake foods and cichlid-specific pellets. Live foods such as fully grown, fresh brine shrimp, small worms and houseflies are ideal.
8. Maintain outstanding water quality with frequent partial water changes.
9. Employ sufficient filtration to cope with these messy eaters.
10. Size doesn’t matter. Any tankmate that is the target of bullying by these fish necessitates the removal of one or the other. The situation will not get better and the victim will certainly become injured, diseased or die.
Should You Keep a Green Terror?
A. rivulatus are easily obtained and frequently stocked in local fish stores. The challenge is to find a pure strain if breeding is intended. Juveniles are inexpensive and typically cost only a few dollars each. This fish is so prolific that you might be able to obtain them for next to nothing from a fellow aquarium club member.
A. rivulatus is a gorgeous fish that is known for becoming quite friendly with their terra firma-based friends. They will be a real conversation piece for those visiting your home. Enjoy your fish!
Stephen G. Noble is a retired postgraduate educator who enjoys sharing the art and science of aquariumkeeping with middle and high school children. He has decades of fish, aquatic plant, reptile and amphibian experience.