Taxonomy & naming
Copadichromis geertsi was described by the cichlid specialist Ad Konings in 1999, in a paper that erected three new Copadichromis species from Lake Malawi published in Tropical Fish Hobbyist (volume 47, number 9, pages 62-84). The type locality is Gome Rock, on the southeastern (Mozambican-Malawian) coast of the lake. The valid name and its authority — Copadichromis geertsi Konings, 1999 — are confirmed by Eschmeyer's Catalog of Fishes and by FishBase, and no synonyms have been proposed; the species has stood unchanged since its description.
The genus Copadichromis was erected by Eccles and Trewavas in their 1989 revision of the Malawian haplochromine genera to hold the "utaka," a Chichewa fisheries term for the shoaling, plankton-feeding haplochromines netted in the lake's open water. Copadichromis is a large and taxonomically difficult genus in which many species are subtle variations on a theme, and Copadichromis geertsi sits among a cluster of deep-living, blotch-flanked utaka that includes Copadichromis virginalis and Copadichromis mloto — a resemblance reflected in its occasional trade name "Virginalis Blotch." Konings distinguished it on a combination of meristic and dental characters and on its distinctive deep-water males.
Morphology
Copadichromis geertsi is a medium-sized, fusiform utaka. The type material gives a maximum of about 5 in standard length (SL) for males and 4.5 in SL for females (Konings 1999, via FishBase); including the tail, mature males reach roughly 6.5 in and females about 6.5 in in total length. The fin counts run to 18-19 dorsal spines and 10-11 soft dorsal rays, with 34-35 scales in a longitudinal series; body depth is contained 2.2-2.5 times in SL and head length 3.1-3.4 times. The flank carries two — sometimes only one — distinct dark spots, the diagnostic "blotch" pattern shared with several related deep-water utaka.
The species is strongly sexually dimorphic in both color and dentition. Immature fish and females are a plain silvery color marked by the two body spots. Mature males transform: the body darkens to deep blue or nearly black, overlaid by a vivid white-to-yellow blaze that runs across the forehead and upper front of the body and continues into the dorsal fin, and the pelvic fins grow very long while the anal fin develops a broad yellow margin. The sexes also differ in their teeth — males bear only unicuspid teeth, whereas in females the outer row of the lower jaw is mostly bicuspid. As in other Malawi mouthbrooders, males carry egg-shaped ocelli on the anal fin used during spawning.
Habitat
Copadichromis geertsi is endemic to Lake Malawi (also called Lake Nyasa and Lake Niassa), and within it is restricted to the southern part of the lake's eastern shoreline. The range runs along the eastern coast from around the Nsinje River and Gome in the south northward to Thundu in Mozambique; the IUCN records it from only about four sites, and its overall distribution is narrow compared with widespread utaka such as Copadichromis borleyi.
It is a fish of the deep intermediate habitat — the transition between rock and open sand. It typically occurs over sediment-rich sandy bottoms with scattered rocks at depths between 25 and 164 ft, and is rarely found shallower than 82 ft, making it one of the deeper-living members of its genus. The lake water at these depths is the same hard, alkaline, well-buffered water that characterizes Malawi's surface layer, with pH on the order of 7.7-8.6 and temperatures in the mid-20s Celsius, though the deep intermediate zone the species favors is cooler and dimmer than the sunlit shallows where most utaka shoal.
Feeding
Like the rest of the utaka guild, Copadichromis geertsi is a zooplanktivore. It feeds on particulate matter taken from the water column — chiefly zooplankton such as copepods — which it picks individually from the open water above and around its habitat rather than grazing the substrate. FishBase places it at a trophic level of about 3.4, consistent with a diet built on animal plankton. Females are sometimes seen foraging in loose groups out in open water, while single fish hang in the water above the bottom between the males' spawning territories. Ecologically the species is part of the offshore plankton-feeding assemblage that converts the lake's zooplankton production into fish biomass — the same guild that supports Malawi's open-water fisheries.
Mating
Copadichromis geertsi has a lek-like breeding system typical of the mouthbrooding utaka. Mature males establish and defend spawning territories down in the deep intermediate zone, at depths greater than 82 ft, where they build conspicuous nests; neighboring males' sites are usually spaced at least about 13 ft apart. Females and non-territorial fish move more freely — females forage in groups in open water and single individuals drift between the males' territories — visiting the nests to spawn. Breeding is not tied to a single tight season: the IUCN notes that breeding occurs year-round, with territorial males present close to the bottom throughout. For a utaka the species is described as relatively peaceful, with males territorial during breeding but not excessively aggressive.
Breeding
Copadichromis geertsi is a maternal mouthbrooder, the standard Lake Malawi strategy. The male constructs a spawning site — a sand bower or "cave crater" — normally under and against a large rock 19.5–78.5 in across, excavating the sand from beneath the rock and heaping it into a semicircular wall around the nest (Konings 1999). A female deposits her eggs at the site and immediately takes them into her mouth; drawn to the egg-shaped markings on the male's anal fin, she collects what appear to be more eggs and the male releases milt, fertilizing the clutch inside her mouth. She then broods the developing eggs and larvae orally without feeding. When the fry are ready, brooding females swim up into shallower water to release their young, which join the schools of juvenile utaka that gather above the nests of the kampango catfish (Bagrus meridionalis) — a setting that affords the fry some protection. Clutch size has not been precisely documented in the wild.
In the aquarium
Copadichromis geertsi is rarely kept in the hobby and is not a fish you are likely to find at a local fish store. It occasionally surfaces in specialist Malawi cichlid circles under the name "Virginalis Blotch," but consistent availability is low and the aquarist wanting this species should expect to source it through cichlid specialty vendors or dedicated breeders. Its comparative scarcity makes the husbandry notes below a combination of what is documented for this species and what is reliably known from closely related open-water utaka — Copadichromis borleyi, Copadichromis chrysonotus, and the broader Copadichromis group.
Tank size is the first consideration. Copadichromis geertsi is an open-water fish that, in the wild, ranges through a dim and largely featureless intermediate zone and covers substantial horizontal distance. A footprint of at least 59 in (roughly five feet) in length, and ideally 71 in or more, is appropriate for a single male with females; a 300-litre tank should be treated as a practical minimum, and more water volume is always preferable. The decor should reflect the species' natural setting: a sand substrate across most of the floor, with a moderate rock structure along one or both ends to provide territory anchors and line-of-sight breaks, but with the central portion left open. Unlike mbuna, utaka do not live in, on, or under rocks — they swim in open water, and a tank crammed with rockwork denies them the space they need and keeps them in a state of chronic stress.
Water chemistry must match Lake Malawi conditions: hard, alkaline, and well-buffered. Target pH 7.8–8.6, general hardness of 10–20 °dH, and carbonate hardness of at least 6–8 °KH. Temperature should be held in the 75–79 °F range consistent with the intermediate depths where the species naturally lives — the cooler end of that range (75–77 °F) is preferable and slightly reduces aggression. Malawi salt mixes are widely available and produce the correct chemistry reliably; plain soft or acidic water is incompatible with long-term health. Efficient filtration and a conservative stocking density are important because the deep, stable chemistry of the natural environment leaves these cichlids with little tolerance for the ammonia and nitrite swings that a bioload-heavy tank can produce.
Copadichromis geertsi is far less aggressive than mbuna (the rock-dwelling Malawi cichlids). In a properly sized tank with appropriate lake conditions, it can be kept in a harem arrangement — one male with two or more females — or in a mixed-species Malawi display alongside other non-mbuna haplochromines of compatible size and disposition. Avoid mbuna entirely in the same tank; the sustained territorial aggression of mbuna is chronic enough to stress utaka even in large setups. Peaceful, similarly sized peacocks (Aulonocara) or other open-water haps make reasonable companions. Mixing multiple male Copadichromis of the same or closely related species in a small tank is inadvisable; in a larger display each male needs a defined territory and enough visual separation from rivals.
Diet in captivity is straightforward. As a zooplanktivore, Copadichromis geertsi accepts high-quality dried foods readily — pellets or flake formulated for omnivore or carnivore cichlids are suitable, supplemented with frozen or live zooplankton such as daphnia, cyclops, and brine shrimp. High-protein, carotenoid-rich foods help maintain the male's color. Like virtually all Lake Malawi cichlids, it should not be fed large amounts of red meat, worms, or high-fat foods that can trigger Malawi bloat, a bacterial condition commonly linked to inappropriate diet. Spawning in a well-conditioned group follows the mouthbrooder pattern described in the Breeding section: the female will carry eggs and larvae in her buccal cavity for roughly three weeks before releasing free-swimming fry. Common keeper mistakes with this and related utaka are overcrowing the tank with rock (removing the open swim space the fish needs), keeping it with aggressive mbuna, providing soft water, and underfeeding quality zooplankton-type foods. Given its rarity, an aquarist fortunate enough to keep a group should also consider participating in a species-preservation network to propagate the line.
Conservation
The IUCN Red List assesses Copadichromis geertsi as Least Concern (assessed 22 June 2018 by Ad Konings, reviewed by Jos Snoeks, with J. Kazembe, P. Makocho and A. Mailosi as contributors; published 2018). This replaces an earlier 2006 listing of Vulnerable; some hobby sources still cite the older Vulnerable status, so the current Least Concern assessment is the one to use. The justification notes that although the species is endemic to Lake Malawi and recorded from only a handful of sites, no widespread major threats have been identified. The population trend is listed as unknown, and no information on population size is available. The species is only rarely taken by the ornamental fish trade (sometimes under the name "Virginalis Blotch"), and the one threat the assessment flags is potential overfishing with chirimila (open-water seine) nets — the same pressure that bears on netted utaka generally.
The lake around it, however, is under accelerating strain. Reviews of the Lake Malawi/Niassa/Nyasa basin document sediment and nutrient loading from a deforesting catchment, intensifying fisheries, climate change, and invasive-species risk as the leading concerns for the system as a whole. None of these is documented as a present danger to this particular cichlid, but as a narrow-range, deep-water endemic of the southeastern lake it has less geographic insurance than the lake's most widespread species, and its long-term security is tied to the health of the lake.