Classic Car Intelligence
  • Species: Aequidens rivulatus

  • Species: Biotodomo cupido

  • Species: Cleithracara maroni

  • Species: Geophagus brasiliensis

  • Species: Laetacara curviceps

  • Species: Aequidens pulcher

South American Cichlids: Part 1, Acaras and Eartheaters

South American Cichlids: Part 1, Acaras and Eartheaters

Of the 1900 or so species of cichlid, no fewer than 450 come from South America. Yet aquarists would be forgiven for imagining that the only South American cichlids in the trade are angelfish, discus, oscars, and rams. In fact the variety of South American cichlids available to the hobbyist willing to search for them is considerable. From dwarf species of Apistogramma to the predatory pike cichlids and giant peacock cichlids, South American cichlids really do offer something for everyone.


Tropical South America is dominated by huge river systems, of which the Amazon and the Orinoco river systems are the best known. In the areas undisturbed by man, these rivers pass through vast tracts of rainforest. Water levels rise and fall depending on the season, and for part of the year the river overruns its banks and floods the forest, allowing the fish to exploit the resources of the 'flooded forest'. Many fish will breed at this time to take advantage of the increased food supply.

Unlike the rivers and lakes of Central America that tend to be hard and alkaline in composition, the water chemistry of most South American rivers tends towards the soft and acidic. In the most extreme cases, blackwater rivers like the Rio Negro can have a pH as low as 5.0 and almost no mineral content at all. These very soft waters are hostile to most kinds of animal life, so that the fishes that live here, including a few cichlids, are very much specialists. By contrast, the typical Amazonian river will contain water that is only slightly acidic to neutral in pH and will have sufficient mineral content to support a rich diversity of animal life include many kinds of fish, molluscs, crustaceans, and insects.

The coastal areas of South America include rivers, lakes, swamps, tidal marshes, estuaries, and mangroves. The fish that inhabit these areas are often very adaptable, and will often be found in water that is hard and alkaline, or even brackish.

Aquarium requirements

The key difference between South American cichlids and cichlids from Central America or the Rift Valley lakes of Africa is the preference for soft rather than hard water. This isn't to say that South American cichlids can't do well in hard, alkaline water; they can. But to get the best from South American cichlids, you want to avoid keeping them in very hard water with a high pH, especially if you intend to breed them. As a rule of thumb, the hardness should be between 5-10 degrees dH, the carbonate hardness around 5 degrees KH, and the pH between 6.0 and 7.0.

If you live in a soft water area, then providing these sorts of conditions will not be difficult. But if you live in a hard water area, you will need to soften your tap water before it is used. There are two ways to do this. The first is to mix a tap water with water that has been run through a reverse osmosis (or RO) filter. The precise ratio of tap water to RO water will depend upon the hardness of your local tap water supply, but even a simple 50:50 mix should work well. In somewhere like London where the hardness is around 20 degrees dH, the resulting mixture will have a hardness of a mere 10 degrees dH, well within the preferred range for most South American cichlids.

The alternative to RO water is rainwater. Rainwater can be collected using a butt placed underneath a gutter. To work well, your roof needs to be clean or the water will end up full of dirt and dead leaves. Although the risk of toxins from air pollution getting into rainwater is small, filtration of the rainwater through carbon would be useful. Once cleaned, the rainwater can be used in the same way as RO water.

Note that once the carbonate hardness gets much below about 5 degrees KH, the aquarium will be more prone to rapid acidification. Large water changes (50% per week) will help here, but the use of pH buffers is recommended in tanks with very soft water.

Blackwater extract can be used to give an aquarium the tea-coloured look typical of blackwater rivers, but blackwater extract has little impact on the hardness and acidity of the aquarium. Peat is sometimes used to soften water and create the acidic conditions favoured by things like Apistogramma. Simply adding peat to the filter in an aquarium produces unpredictable results and is best avoided. Instead, use peat inside a simple box filter to treat buckets of water prior to adding that water to the aquarium. That way you can test the pH and hardness before it is added to the tank, and adjust or buffer as required.

When adjusting the water chemistry of your aquarium it is critical to remember that fish do not like rapid changes in pH or hardness, even where those changes go in the "right" direction. Rapidly softening and acidifying the aquarium will stress your fish, making them more prone to disease and can potentially kill them outright. It is much better to aim for stable water conditions. Moderately hard, neutral water will suit most South American cichlids just fine, so there's no real need to create inherently unstable very soft and acidic water conditions even though these cichlids might inhabit such waters in the wild.

Water quality, on the other hand, is far more important. Few South American cichlids tolerate polluted water, and most are acutely sensitive to nitrate as well as nitrite and ammonia. High levels of nitrate cause a variety of problems, including hole-in-the-head disease. Large, regular water changes are essential to keep nitrate levels manageable. Ideally, aim for a nitrate concentration of less than 20 mg/l, and certainly no higher than 50 mg/l.

Social behaviour

The social behaviour of South American cichlids varies. A few species are extremely aggressive, most notably the green terror Aequidens rivulatus. But most are much less aggressive than Central American cichlids, at least outside of spawning, and consequently tend to make better community fish. With only a few exceptions, South American cichlids can be kept alongside characins and catfish of similar size without any problems. Silver dollars and plecs are probably the classic companions for most species, not only working well with these fish, but also coming from the same part of the world.


The acaras are a vaguely-defined group of medium-sized cichlids that are widely distributed across tropical South America. Three genera are of particular importance to aquarists, Aequidens, Laetacara, and Cleithracara. Most acara are predatory, feeding primarily on worms and insect larvae. The larger species will also eat very small fish such as neons. Acara tend to be sensitive to poor water quality, and will not look their best in crowded, polluted tanks. In good condition though, some of these species are very attractive, and for the post part they can make good cichlids for the beginner wanting something colourful and not too difficult to keep.

Aequidens spp. tend to be territorial and sometimes very aggressive, to the degree that they are more like Central American cichlids in terms of husbandry than most of the other South American cichlids. Two species are commonly traded, the blue acara Aequidens pulcher and the green terror Aequidens rivulatus.

Blue acaras are quite large (around 15 cm) cichlids with deep, oval bodies. Basic colour is blue, though this varies with mood. In breeding condition they are steel-blue with brilliant turquoise spots and squiggles across the flanks, face, and fins. Dark vertical bands will be apparent from time to time, and there is a round blotch about halfway along the flank. Males are bigger than females and more colourful. Blue acaras inhabit a variety of waters and will do well across a broad range of water chemistry values, from slightly soft and acidic to hard and alkaline. They do not like very high temperatures though, and show be kept around the 20 degree C mark, ideally alongside subtropical fish that enjoy similar conditions. Blue acaras are essentially peaceful but territorial. In a spacious tank with plenty of hiding places they will behave themselves very well, becoming tame quite quickly.

The green terror is very similar to the blue acara in looks but larger (to 20 cm) and more colourful. The flanks are almost entirely covered with green-blue spots, as are the unpaired fins. There are also prominent green-blue squiggles on the face. A thick orange fringe marks the dorsal and tail fins. Compared with blue acaras, the vertical bands on the flanks are much less apparent but the black blotch halfway down the flank is usually very clearly visible. Like the blue acara, the green terror is sexually dimorphic, the male being bigger and more colourful. The green terror appreciates slightly warmer water than the blue acara but otherwise shares the same tolerances. The main difference as far as the aquarist is concerned is its aggression. This species has justly earned its common name, being one of the more aggressive cichlids in the hobby. Stable pairs are best kept alone or in large tanks with other fish able to look after themselves.

The port acara Cichlasoma portalegrense is one of the best cichlids for the inexperienced hobbyist. It is hardy, tolerant of wide range of conditions, peaceful, and easy to breed. In the early days of the fishkeeping hobby, it was very widely traded but in recent years it has become much less common. This is probably because it isn't terribly colourful, basically greenish-brown with blue-green speckles on the flanks and fins. There is a dark band along the midline of the fish and two black blotches, one midway along the body and another on the base of the tail. The pectoral fins are yellow, and the other fins red. Colours do vary with mood though, and this fish is outgoing and not at all shy, making it a fun pet in a tank alongside things like loaches and catfish. Maximum size in aquaria is around 10 cm. Does best in relatively cool conditions, around 18-20 degrees C.

The flag acara Laetacara curviceps is a small cichlid (8-10 cm) ideally suited to the peaceful community tank. While territorial, it will ignore midwater and upper-level fish. When breeding they will chase other bottom-dwelling fish though. Colouration is remarkably variable and depends upon mood, but this fish is usually green to bluish-grey with blue-green speckles on the face, flanks and fins. An irregular dark band runs along the midline of the body from the eye to the base of the tail. Males are bigger and have longer fins than females.

The keyhole cichlid Cleithracara maronii is another superb community tank cichlid. These fish are even more peaceful than flag acaras. Maximum size in aquaria is around 10 cm, though wild fish can be a little larger. Keyhole cichlids have a honey-coloured body marked with a dark vertical band running through the eye and a dark spot about two-thirds of the way down the flank. Sexing these fish is difficult, but males tend to be larger and often have longer anal fins. This is a shy species that appreciates a densely planted tank with plenty of shade. Do not mix with aggressive or nippy tankmates.


The eartheater -- or geophagine -- cichlids are very interesting cichlids that specialise in sifting sand and mud while searching for food. As such these fish need an aquarium that combines rocky hiding places with open areas of sand or fine gravel. Their constant digging can make the aquarium rather messy, so a strong filter is needed to remove silt and detritus. Robust plants are generally unharmed, particularly epiphytes like Java fern and Anubias, but many aquarists prefer to use plastic plants in tanks with eartheaters. Several eartheaters are also unusual among South American cichlids in being mouthbrooders, a mode of reproduction otherwise confined to the African cichlids. On the whole eartheater cichlids tend to be rather large, sometimes aggressive, and always sensitive to poor water conditions. So while fascinating animals, they are best thought of as cichlids for the more experienced hobbyist rather than the absolute beginner.

The cupid cichlid Biotodoma cupido is a relatively small but somewhat pugnacious eartheater best suited to robust community tanks with things like catfish, loaches, and silver dollars. They are basically pink in colour but the flanks are iridescent, so their colours vary dramatically depending on the light. In good condition these fish are extremely attractive. Sexual differences are slight, though males tend to have more strongly developed markings on their faces. Maximum size is about 12 cm.

The pearl cichlid Geophagus brasiliensis is one of the larger eartheaters. Maximum size in the wild is at least 25 cm, but in aquaria they remain much smaller. Pearl cichlids are found in coastal rivers including brackish water areas. While the addition of salt to the aquarium is not essential, this species should not be kept in soft, acidic water but in water that is neutral to slightly alkaline and moderately hard. Juveniles are drab green-brown animals, but the adults colour up remarkably. The ground colour is pinkish-green, lighter below and darker above, with blue, green, or violet speckles on the flanks and fins. Males are bigger than females and when mature have prominent nuchal humps. While this species is territorial, in a spacious aquarium they are tolerant of tankmates and make good additions to the robust community tank.

The demon eartheater Satanoperca jurupari is, despite its name, quite a peaceful species outside of breeding. It is quite large though, up to 30 cm in length, so needs to be kept in a roomy aquarium. Demon eartheaters have a distinctively large head and sloping profile. The mouth is quite large, and these fish are very effective diggers. Sexual dimorphism is not present in this species: both sexes are of similar size and share the same green with green-blue speckles colouration. A good community species when kept with midwater and upper-level tankmates as well as retiring catfish such as plecs. This species is referred to as a "primitive" mouthbrooder. Eggs are placed in a nest and guarded by both parents until they hatch. The fry are then brooded by both parents who take turns holding them in the front of the mouth (rather than the throat, as is the case with African mouthbrooders).

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