Taxonomy & naming
Haplochromis teunisrasi was described in 1981 by the Dutch ichthyologists Frans Witte and Els L.M. Witte-Maas in a paper bearing the telling title "Haplochromine cleaner fishes: a taxonomic and eco-morphological description of two new species" (Netherlands Journal of Zoology 31(1): 203–231), the first instalment of the Leiden team's long revision of the Lake Victoria haplochromines. The two species treated together were Haplochromis teunisrasi and its close relative Haplochromis cnester, both diagnosed as ectoparasite-feeders. The holotype (RMNH 28258) and a series of paratypes are held in the Naturalis collection at Leiden, with one paratype (BMNH 1981.1.16.116) in the Natural History Museum, London. The type locality is the west side of the Mwanza Gulf, between Nyamatala Island and Hippo Island, Lake Victoria, at 31–43 ft depth. The species belongs to the great Lake Victoria species flock of haplochromine cichlids (tribe Haplochromini), the explosively radiated assemblage of several hundred endemic forms. Like most of that flock it is retained in Haplochromis in the broad, deliberately conservative sense defined by Martien van Oijen's 1996 generic revision, which — pending a clearer phylogeny — kept the bulk of the Victoria haplochromines in a single genus rather than splitting them prematurely. Some workers place predatory and specialised Victoria haplochromines in segregate genera, but no widely accepted reassignment of teunisrasi exists, and Haplochromis remains the standing combination.
Morphology
This is a small cichlid: the type series reaches about 4 in in standard length. Witte and Witte-Maas characterised Haplochromis teunisrasi as slender — body depth roughly 30–35% of standard length — with a relatively short, gently curved head, a build that sets it apart from the stockier, more generalised habitus of its sister species Haplochromis cnester. The dentition is the diagnostic feature tying the two cleaner species together: closely set, unequally bicuspid teeth with an obliquely truncated major cusp in the outer row, and inner teeth arranged in two to four rows. As in essentially all haplochromines, the species is a maternal mouthbrooder, and sexual dimorphism follows the familiar pattern: breeding males develop bright nuptial coloration and carry ocellated "egg-spots" (egg-dummy markings) on the anal fin, while females and non-breeding fish are comparatively drab and silvery. No life colour photograph of teunisrasi is in general circulation, and the published account rests on preserved material, so the fine detail of the male nuptial pattern is not well documented.
Habitat
Haplochromis teunisrasi is endemic to Lake Victoria, the largest of the African Great Lakes and the centre of one of the most spectacular vertebrate radiations on Earth. The type material and the closely studied populations come from the Mwanza Gulf in the Tanzanian (southern) part of the lake. The species is a fish of the open, rather exposed offshore bottom rather than the rocky inshore: FishBase and the original description record it over soft mud substrates at depths of about 26–49 ft. Lake Victoria is a shallow, warm, well-mineralised lake; its surface waters are typically alkaline, with pH commonly in the range of about 7.2–9.0 and temperatures around 73–81 °F, and the offshore mud bottoms this species frequents are seasonally subject to low oxygen. Within that setting teunisrasi belongs to the offshore mud-dwelling community of haplochromines that, before the ecological upheaval of the late twentieth century, partitioned the lake bottom among dozens of trophically specialised species.
Feeding
The feeding ecology is what makes this fish remarkable. Witte and van Oijen's analysis of Lake Victoria haplochromine trophic groups classifies Haplochromis teunisrasi as a parasite-eater — one of a tiny guild of cichlids that exploit the external parasites of other fishes. Gut contents of the cleaner species consist mainly of carp lice (the branchiuran crustaceans Argulus and Dolops) and leeches (Helobdella), with small additional amounts of zooplankton and diatoms. The inference drawn by the describers is that these fishes obtain their prey by cleaning other fish — removing ectoparasites from the bodies of larger hosts, probably mainly catfishes — a behaviour analogous to the cleaner wrasses of coral reefs but evolved independently within the Victoria flock. The unequally bicuspid, obliquely truncated teeth are read as an adaptation for plucking attached parasites. Direct underwater observation of the cleaning act in the wild is sparse, so the behaviour is reconstructed largely from diet and dentition rather than from filmed interactions; it remains one of the more intriguing and least-witnessed feeding strategies among the lake's cichlids.
Mating
No courtship or pair-formation behaviour has been described specifically for Haplochromis teunisrasi. Its reproductive biology is inferred from the Lake Victoria haplochromine pattern, which is well established across the flock: these are polygynous maternal mouthbrooders in which the sexes lead largely separate lives outside spawning. Males in breeding condition acquire vivid nuptial coloration and display to females over a loosely defended patch of bottom; the anal-fin egg-spots function as a lure during the spawning sequence, when the female snaps at the dummies and so takes up the male's milt to fertilise the clutch already in her mouth. Mate choice on male colour is a central driver of the rapid speciation that produced the Victoria flock. For teunisrasi specifically the territorial and courtship details are unrecorded, and the account here should be read as genus-typical rather than observed.
Breeding
Like virtually all Lake Victoria haplochromines, Haplochromis teunisrasi is a maternal (ovophilous) mouthbrooder: the female takes the fertilised eggs into her buccal cavity and incubates them there, releasing free-swimming fry after the yolk is absorbed and continuing to shelter them in her mouth when threatened in the early days after release. Clutch sizes have not been published for this species; small Victoria haplochromines of comparable size typically carry on the order of a few dozen eggs (roughly 20–60), and that figure is offered here as a genus-typical estimate, not a measured value for teunisrasi. Parental care is entirely maternal — there is no paternal or biparental brood care in this group. Spawning seasonality, fry size at release, and developmental timing are undocumented for the species.
In the aquarium
Haplochromis teunisrasi is essentially absent from the aquarium hobby. It is a small, cryptically coloured, deep-mud offshore specialist with a narrow and bizarre diet — ectoparasites cleaned from other fishes — that does not translate into a maintainable captive animal, and it has no history in the trade. It should not be confused with the colourful "Lake Victoria Haplochromis" sold under trade names, which are different, hardier species. Were a specialist ever to keep it, the general requirements of Victoria haplochromines would apply: hard, alkaline water (pH around 7.5–8.5, moderate to high hardness), a temperature near 75–79 °F, a soft sand or fine substrate, robust filtration and frequent water changes, and the understanding that males are aggressive toward one another in the typical haplochromine way. The obligate parasite-cleaning diet would make it impractical to feed properly. For all realistic purposes this is a wild species of scientific rather than hobby interest, and the honest answer is that it is not an aquarium fish.
Conservation
The IUCN Red List assesses Haplochromis teunisrasi as Critically Endangered under criterion C2a(ii), assessed on 31 March 2010 by Witte, de Zeeuw and Brooks. The assessment reflects the wider catastrophe that overtook the Lake Victoria haplochromine flock: following the deliberate introduction and explosive upsurge of the predatory Nile perch (Lates niloticus) from the 1980s, together with eutrophication, declining water clarity and intensified fishing, an estimated several hundred endemic haplochromine species declined sharply and many are thought to have gone extinct. Offshore, mud-dwelling specialists such as teunisrasi were among the hardest hit, and a narrowly specialised parasite-cleaner dependent on a healthy community of host fishes is doubly exposed when that community collapses. Partial recoveries of some haplochromine species have been documented in the Mwanza Gulf since the partial decline of the Nile perch, but they have often been accompanied by dietary and morphological shifts, and there is no published confirmation that this particular species persists in numbers. It carries no CITES or CMS listing. Its status should be read against the backdrop of Lake Victoria as one of the most heavily impacted large-lake ecosystems on the planet.