Congochromis dimidiatus

Congochromis: named for the Congo basin, plus chromis, a name the ancient Greeks used for a fish.

dimidiatus: Latin for 'halved' or 'divided in two'. Pellegrin didn't explain the name.

Described from Bangui (spelled Banghi in the original description) on the Ubangi River in the Central African Republic.

Museum records place it widely across the central Congo basin in the Republic of the Congo and DR Congo, from the Ubangi and Sangha rivers south to Lake Tumba and the Tshuapa River around Boende, and east to Kisangani. Most of these fish were identified before Congochromis was separated from Nanochromis in 2007, and before Congochromis robustus (2012) and C. rotundiceps (2022) were described, so some may belong to other species.

FishBase treats a record from Chad as questionable, and also lists it from the upper Chari in the Central African Republic, in the Lake Chad basin. Reports from Gabon and Cameroon refer to Parananochromis brevirostris.[5][9]

Stiassny and Schliewen (2007) describe it as a fish of larger rivers and lakes, where C. sabinae lives in small rainforest streams. Several museum records come from small forest streams and swampy pools, though, and no detailed habitat data have been published for it.[1]

A tank with a base measuring 60 ∗ 30 cm24 ∗ 12 in or similar is the minimum for a single pair, for breeding or general care. More than one pair needs a much larger tank.

Use a soft, sandy substrate, as this species lives on the bottom, and provide caves as potential spawning sites. Clay flowerpots, halved coconut shells or short lengths of plastic pipe all work, along with driftwood roots and branches arranged to give plenty of shaded spots.

Dried leaf litter such as beech, oak or Indian almond leaves adds cover and lets colonies of microorganisms develop as it breaks down, giving the fry a source of food.

Keep the lighting fairly dim. Plants that tolerate these conditions include Anubias, Microsorum, Taxiphyllum and potted Cryptocoryne species, and a few patches of floating plants help to diffuse the light. Gentle filtration with a little surface movement is enough.

Congochromis species need stable water conditions and should never be added to an immature tank.

Temperature: 22 – 25 °C72 – 77 °F

pH: 6.0 – 7.0

Hardness: 5 – 8 dGH[3]

In the wild Congochromis species feed on the bottom, taking detritus, plant material and small invertebrates.

In the aquarium, offer a varied diet of good-quality, fine-grade prepared foods, including some with a high proportion of Spirulina or similar. Add live or frozen bloodworm, Daphnia, Artemia and mosquito larvae now and again.

It can be kept in a community tank if the tankmates are chosen with care. Good choices include small schooling fishes such as Ladigesia roloffi or Lepidarchus adonis, small African barbs and Aplocheilichthys killifishes. It can also be kept with peaceful South American characins, Otocinclus or smaller Corydoras catfishes, and Southeast Asian cyprinids such as Trigonostigma or Boraras species.

Other cichlids are best avoided unless the tank is very large, and larger bottom-dwelling species should be left out entirely, as they compete for territory and food.

For breeding, keep a pair on its own or with a group of small-mouthed, non-predatory dither fish such as Nannostomus species. It isn't especially aggressive, but males are territorial and a single pair is best in most tanks. A group may coexist in a larger one.

Females are more colourful than males, with a violet flush to the belly and one or more black spots in the rear of the dorsal fin. Adult males are larger and more orange overall, with a slightly spade-shaped tail and short extensions to the dorsal and anal fins.

Unlike females of C. sabinae and C. squamiceps, females of C. dimidiatus have no patch of silvery scales around the genital papilla (Lamboj, 2005).[2]

Congochromis species are monogamous, bi-parental cave spawners and breed readily in aquaria if their basic needs are met. Soft water is advisable for breeding, and an air-powered sponge filter set to turn over gently is the best filtration for a breeding tank.

Pairing is usually easy, and placing an adult male and female together in the breeding tank is often enough. The male may chase the female at first, but injuries haven't been reported. If you start with a group of young fish, be ready to move the others once a pair forms.

The female starts the courtship. Once in condition she takes on breeding colours and displays to the male by bending her body into a U shape, showing him her violet belly, while quivering rapidly. A receptive male shows more red to orange on the lower front part of the body, and in both sexes the body colour pales and the dark lateral stripe fades. The pair then choose a concealed spawning site and often dig their own entrance to it.

After spawning the female stays in the cave and cares for the brood alone, while the male is driven out and defends the surrounding territory. The eggs hatch after about three days, depending on temperature, and the fry are free-swimming around 8-9 days after spawning.

Once they are foraging outside the cave they can take Artemia nauplii, microworms or banana worms, Cyclops and Daphnia. Parental care lasts 5-6 weeks, though in some young pairs the male turns on the female and she has to be removed.[4]

Described as Pelmatochromis dimidiatus by Pellegrin in 1900, and later moved to Nanochromis, the name it carries in most older aquarium literature.

Schliewen and Stiassny (2006) recognised two informal groups within Nanochromis, the nudiceps group and the squamiceps group. Stiassny and Schliewen (2007) then moved the squamiceps group, including this species, into the new genus Congochromis.

Congochromis differs from Nanochromis in having only the last three to five pored scales of the upper lateral line alongside the dorsal-fin base, a fully scaled nape and a partly scaled chest and cheek, fairly stout and widely spaced unicuspid jaw teeth, and a small supraneural bone. Internally it has four pores in the dentary laterosensory canal, no laterosensory canal in the anguloarticular and six pores in the preopercle canal (Stiassny and Schliewen, 2007).

Six species are now recognised: C. dimidiatus, C. pugnatus, Congochromis robustus, C. rotundiceps, C. sabinae and C. squamiceps. C. rotundiceps, described from around Malebo Pool in 2022, has a wider interorbital (28.3-32.1% of head length, against 23.8-28.2% in C. dimidiatus) and a wider preorbital (39.0-41.5% of head length, against 32.3-38.5%) (Wingi et al., 2022).

In C. dimidiatus and C. squamiceps the dark stripe along the flank runs into the caudal fin, while in C. sabinae it stops short of it (Lamboj, 2005).

Within the family, Congochromis belongs to the chromidotilapiine cichlids and is most closely related to Nanochromis. Preliminary DNA data mentioned by Stiassny and Schliewen (2007) also grouped Chromidotilapia schoutedeni and Limbochromis robertsi with the two genera.[1][2][6][7]