Nanochromis – Genus of West African Dwarf Cichlids

Nanochromis parilus female

Nanochromis is a genus of small, slim-bodied cichlids from the Central Congo Basin in Western Africa. They’ve been known to aquarists for many years and are prized by experienced fish keepers. They are attractive fish with a high degree of sexual dimorphism. Nanochromis are cave spawners that usually form strong pair bonds when breeding. Nanochromis originate from very soft, acidic waters and may need the same conditions to thrive in an aquarium. Some species are adapted to living in fast water and are captured from areas of rapids. All species are omnivores and vegetative material should be included in their diet.

What distinguishes a Nanochromis?

The characteristics that define the genus include anatomical measurements such as the number of scales on the caudal peduncle, bone structure, and other technical features. Rather than list the specifics which are best understood by ichthyologists, here are some general observations on the genus.

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Male and female pair of Nanochromis transvestitus
Female Nanochromis transvestitus displaying her round red abdomen to her mate. While most Nanochromis males are more colorful than females, in this species females are more colorful.
  • Nanochromis are very slender in proportion to their length. Some species can reach a total length of nearly 4 inches but most are smaller than this..
  • They exhibit strong sexual dimorphism. Males usually have more colorful markings along with longer fins and a larger overall size.
  • Females are shorter in length and normally have shorter and rounder fins.
  • Females exhibit obvious round bellies that range from red to violet and the color varies from faint to vibrant.
  • All species are found only in the Congo Basin

History of the Genus Nanochromis

The first Nanochromis species, N. nudiceps, was described in 1899 by the Belgian-British zoologist George Albert Boulenger, who was a very prolific ichthyologist who described 1,096 species of fish. He described the genus as Pseudoplesiops which, unfortunately, had already been used in 1858 for a species of marine fish making it invalid. The genus Nanochromis was subsequently erected by Pellegrin in 1904 as a replacement name for Pseudoplesiops. That established the genus with N. nudiceps as the type species. Over the years the genus has gained and lost species through new discoveries and reclassifications.

Historically, several other groups of species were included in Nanochromis and it was always known that the genus would lose species to future reclassification. In 1987 the British ichthyologist P. H. Greenwood split two groups out from Nanochromis to form Limbochromis for a larger and obviously different species and Parananochromis for several species that were much larger and differed morphologically. Then, in 2007, Melanie J. Stiassny and Ulrich Schliewen erected the genus Congochromis to house a group of species that were always recognized as anatomically different. You will find much more information in: Congochromis, a New Cichlid Genus (Teleostei: Cichlidae) from Central Africa,

Nanochromis Species List

As of 2022, there are 8 described Nanochromis species. 4 of these are found only in the rapids and are adapted to living in high current areas. Three of the others are found in lakes and the fourth is found both in the rapids and in quiet waters.

Native Distribution of Nanochromis

This Congo River Basin map was modified to outline in green the approximate area where Nanochromis species are found. This map was produced by and provided courtesy of Kmusser, CC BY-SA 4.0, via Wikimedia Commons

Nanochromis are only found in the “Cuvette Centrale” and the rapids of the lower Congo River. The Cuvette Centrale lies at the heart of the central Congo basis which is the second-largest rainforest in the world. With 60″ – 80″ of annual rainfall the river runs through some of the densest rainforests anywhere. There are few settlements and this is some of the wildest land on the globe. Consequently, we have an incomplete picture of the species, habitats, and natural history of the genus.

Most Nanochromis species have been collected from the main channels of the large rivers, primarily the Congo itself. Four of the eight described Nanochromis are known only from the rapids of the lower Congo between the Malebo Pool and the town of Inga. N. nudiceps, the type species, is found in these lower river rapids but was described as coming from “Kutu”, a small Congolese town located in the inner Congo basin (Cuvette Centrale) at the junction of the outlet of Lake Mai Ndombe (formerly Lake Leopold II) with the Lukenié-Fimi River,

Lake Mai Ndombe is a large (85 mi long and up to 35 mi wide) and very shallow lake (average depth of 10 ft) with predominantly sandy beaches and with a few stretches of rocky shorelines. The lake is surrounded by rainforest and swamps and its fish fauna is largely unsampled. the lake’s water is very soft and acidic with pH measurements typically about 4.0 – 4.5. It is home to two species, N. transvestitus, and N. wickleri. These two species are lake dwellers and are not as rheophilic as the other members of the genus.

Nanochromis Natural Habitats

It must first be noted that I’ve found very little precise information about the natural habitats of Nanochromis. Reportedly, they are found in large rivers and lakes and may be absent from smaller streams. I don’t know if this is because they aren’t found in smaller waters, if it indicates a lack of sampling, or if it is from a lack of publishing collection information. While there’s not a lot of info available, the books and species description papers I’ve read do provide some information.

Nanochromis parilus female
Nanochromis parilus female showing vent tube prior to spawning

4 of the 8 Nanochromis species are rheophilic species found in fast-flowing water. These species, N. consortus, N. minor, N. parilus, and N. splendens, were described in 1976 based on collections taken in and near the rapids of the lower Congo. They were collected by using the piscicide rotenone, a poison that kills all the fish in the river. Following the rotenone application, all possible fish carcasses were gathered which resulted in a collection of over 7,000 fish from 129 species.

A collection on this scale couldn’t provide detailed habitat information on the sampled species. The rotenone collections were conducted across fairly large areas with variable depths, usually 3 – 6 ft deep. The fish were collected after they floated to the surface so there are no accounts of the exact habitat where any particular species preferred to live. The Nanochromis may have been over the sand, close to rocky shoals, or anywhere within the sampled area. Water conditions for these collections were more neutral than the extremes of the waters in the Cuvette Centrale. pH ranged from 6.5 to 8.5 in fairly soft water with temperatures ranging from 76°F to 84°F.

New collections reported in 2011 (Schwarzer, Misof, Ifuta, & Schliewen) provide more precise habitat descriptions for the rheophilic species. The authors report that Nanochromis are only found in the rapids themselves where the substrate is either sand or bedrock. They are not found in the sections of slow-moving water between the rapids.

It’s difficult to be sure of the range of Nanochromis nudiceps. In the 1899 description, the type locality was listed as Kutu, Lake Leopold II, Zaire (Lake Mai Ndombe). In 1964 they were reported to have been collected in Lac Tumba but, to the best of my knowledge, this has never been confirmed. These reports would indicate a lacustrine-aligned species but this is not confirmed and it is generally grouped with the more rheophilic members listed above.

The two lacustrine species, N. transvestitus, and N. wickleri are found in Lake Mai Ndombe where N. transvestitus is said to inhabit waters to a depth of about 3 ft in areas with sandy substrate distributed among rocky patches. N. wickleri is found over rocky areas at depths of 3-6 ft. The lake is very acidic with a pH of about 4.0 and the water is clear but stained dark with high humic content. It’s reported that the water is so dark colored that at a one-foot depth you cannot see your hand in the water. It seems that the substrate varies from soft mud to solid rock. Unfortunately, I’ve not seen any published accounts specific to Nanochromis habitats.

Nanochromis Aquarium Care

Although we don’t have extensive information about their natural habitats, aquarists have many years of successfully keeping and breeding them in home aquaria. Generally speaking, aquarium care is the same for all species in the genus. They are all cave spawners that form pairs for breeding. These pairings may last on a long-term basis or the pair bond might not last beyond a single spawning attempt.

Setting up a Nanochromis Aquarium

The best habitat for Nanochromis is a mixed layout that combines open areas with cover areas. Sand makes the best substrate as the fish love to dig through it. Rockwork, driftwood, or thickets of plants are all possibilities for areas of cover. You need to make sure there are multiple places where a bullied fish (usually the female but not always!) can hide. Nanochromis are cave spawners so be sure to incorporate several caves into the layout. The best caves have a small opening that’s barely large enough to allow the female to get through. They really prefer dark secluded spots for spawning. Often the female will move the substrate to completely block the entrance to the cave, sealing herself in. Don’t worry, this is normal and she won’t starve or suffer.

It’s unlikely that there are many aquatic plants in their native waters but I’m a big fan of adding live plants to my tanks. They help to stabilize water chemistry, their leaves are covered with a microbial film that fry can feed on, as they break down in the tank they may be eaten by the fish, and they provide great cover and security. I especially like to have a layer of floating plants covering the surface to help cut down on light intensity. Nanochromis come from waters that are stained dark with tannins which reduces light penetration and makes their habitats very dark. Placing them in a brightly lighted aquarium is not advised.

Learn more about appropriate plants in our Complete Guide to Live Plants in Dwarf Cichlid Aquariums.

Water conditions

The water conditions you need to provide vary depending on what species of Nanochromis you have. N. consortus, N. minor, N. parilus, and N. splendens are from the Lower Congo where the water conditions are close to neutral. They should do fine in an aquarium with pH ranging from 6.0 – 7.5.

The other Nanochromis originate from waters that are very soft and acidic. In some locations, the water is so soft that it can’t be measured. Ph values as low as 4.0 are typical and the water is very high in humic content. They are found in an area that lies on the Equator and temperatures are constant year-round, likely staying in the mid to upper 70°F range. For these species you must provide very soft and acidic water to keep them in good health. Hardness should be of no more than 2 dGH, pH 4.5 – 5.5, and temperature of 76°F – 80°F.

Behavior

Most Nanochromis are very aggressive with conspecifics, especially within the confines of an aquarium. While a group of young fish rarely presents difficulties, it’s usually best to keep adults in pairs. Generally, it’s easy to tell the sex making it easy to get a male/female pair. However, just having one fish of each sex doesn’t guarantee they will be a compatible pair so you must plan accordingly.

Assuming you have a male and a female that are not bonded, you need to plan ahead in case there are compatibility issues. Sometimes, they will accept each other without any drama which is always great. However, there are times when they seem to be incompatible with one (usually the male) incessantly chasing the other, weaker fish. These cases often end in death unless you take steps to intervene.

It’s best to create refuge areas that are so dense that the dominant fish doesn’t bother trying to chase the weaker out. This can be dense thickets of plants or complicated rockwork areas with multiple escapes from any single spot. I don’t hesitate to use spawning mops to add temporary dense cover. A few floating and sinking mops will create shelter areas very quickly. Spawning mops are easy to make all you need is some yarn.

It can be pretty stressful for you and your fish during these types of aggressive acclimations. However, if you can find a way to keep them in the tank together they should eventually show interest in having a compatible relationship. As always, I caution that each fish has an individual personality and behavior may vary widely from fish to fish. Undertaking these “forced pairings” is not recommended for the novice hobbyist!

When you are using dense cover to force a pair, you need to make sure the weaker fish gets a full ration of food. The tight hiding places they seek out are not usually easy places to get food into. Live baby brine shrimp can be very helpful as they will swim into all parts of the tank. Pay attention and try to make sure the weaker fish is getting enough food. Only when a female is well-fed will she be receptive to a male for possible spawning. It takes a lot of energy to produce eggs which means plentiful high-quality food.

Feeding

Generally, Nanochromis are easy to feed in the aquarium. They are omnivores and will eat almost any food offered. While they love high-protein foods, their natural diets include a lot of vegetation and they require roughage in their diet to stay healthy. Since they are strongly oriented to the bottom, I use sinking pellets and wafers as opposed to flake foods. There are many high-quality prepared sinking foods that are suitable for use. I generally use a balanced pellet for daily feeding and supplement it with a piece of algae wafer every other day or so.

Nanochromis will gorge themselves on live foods when they are offered. If I am trying to condition them for breeding I feed a lot of baby brine shrimp, daphnia (when I can get it), and mosquito larvae. They really love black worms or white worms but I avoid feeding the later except for an occasional single worm. I believe that a diet rich in these worms will not lead to long-term healthy fish. They have too much protein and fat without any roughage.

I don’t usually recommend feeding frozen foods to Nanochromis. The fish love them and will eagerly eat them when offered. However, I think most frozen foods are best for carnivorous fish and aren’t as good for omnivores. If you are feeding frozen food regularly be sure to have as many or more feedings of vegetable-based foods. As a supplement, frozen foods are fine but I’d avoid a steady diet of them.

Breeding

All known Nanochromis are biparental cave-spawning fish. They form male/female pairs that work together throughout the breeding cycle from site preparation to raising the fry. The female will typically tend the eggs and larval fry while hidden away in a cave. The male will patrol a larger perimeter outside the cave to keep the female safe. After the fry become free-swimming, the male will usually participate in caring for the fry.

Generally, spawning success occurs by introducing a pair into a properly prepared aquarium and giving them time to acclimate to each other. Feed them well and provide frequent water changes and they will eventually initiate spawning behavior. While some fish seem to spawn in short order, others may take a long time.

Raising Nanochromis fry is usually a pretty straightforward endeavor, The female will escort the school of fry around the tank as they progressively take larger foods. Newly hatched brine shrimp and micro worms are great foods. they will constantly graze on the substrate and hard surfaces in the tank, eating small bits of micro-food. As they grow you can introduce prepared foods. The parents will usually care for the fry for a month or more until they gradually lose interest. It’s often possible to raise the fry with the adults without any conflicts until the pair is ready to spawn again.

Where to buy Nanochromis

Fish in the genus Nanochromis are not particularly rare but that doesn’t mean they are common. If you are flexible about the species you can often find one or more species available from online specialty fish sellers. However, if you are seeking a particular species you might have to search long and hard as some species are rarely offered for sale.

It’s pretty rare to find Nanochromis in a pet store so you are best off searching online. We have specific suggestions in our Guide To Buying Dwarf Cichlids.

Learn more about these Nanochromis species:

Male Nanochromis parilus in an aquarium

Nanochromis parilus

Nanochromis parilus is a <abbr class='c2c-text-hover' title='Fishes and other creatures that prefer to live in…

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References

Most of the information I provide on this website comes from books and websites. While I don’t provide specific citations, these are the sources for most of my information.
South American Books:
Mergus Cichlid Atlas Volume 1 & Volume 2 by Dr. Uwe Römer
South American Dwarf Cichlids by Rainer Stawikowski, I. Koslowski and V. Bohnet
Die Buntbarsche Amerikas Band 2 Apistogramma & Co. by Ingo Koslowski, Translation by Mike Wise
South American Dwarf Cichlids by Hans J. Mayland & Dieter Bork
American Cichlids I – Dwarf Cichlids by Horst Linke & Dr. Wolfgang Staeck
West African Books:
The Cichlid Fishes of Western Africa by Anton Lamboj
African Cichlids I – Cichlids From West Africa by Horst Linke & Dr. Wolfgang Staeck
Websites:
Apisto sites – the home page of Tom C – Global authority for identification and classification of apistogrammas
Apistogramma.com – An excellent international forum with expert members who gladly share their knowledge.
Much more information is available in our complete exploration of dwarf cichlid information resources.