Taxonomy & naming
Paretroplus petiti was described by the French ichthyologist Jacques Pellegrin in 1929, in the Bulletin de la Société Zoologique de France, on a single specimen — the holotype, MNHN 1928-0282, which remains the only known example of the species. The type locality is the Maintimaso River near the town of Maintimaso (about 16°10'S, 46°43'E) in what was then Majunga (Mahajanga) Province, in the lowlands of northwestern Madagascar; John Sparks (2002) discussed the type locality and the uncertainty surrounding it. The genus Paretroplus was erected by Pieter Bleeker in 1868 for Madagascar's deep-bodied cichlids, with Paretroplus damii as its type species; it belongs to the subfamily Etroplinae, the Gondwanan relict lineage whose only other members are the Etroplus and Pseudetroplus cichlids of India and Sri Lanka. Within Paretroplus, petiti sits in the group of high-bodied, disk-shaped species collectively called 'dambas' (alongside Paretroplus dambabe, P. maculatus, Paretroplus maromandia, Paretroplus menarambo, and Paretroplus polyactis). The species' taxonomic history is unusually tangled. Because the holotype is a juvenile and poorly localized, the name 'Paretroplus petiti' was for decades applied to a large, handsome damba from Lake Kinkony in the Mahavavy du Sud drainage; when Sparks described that Kinkony fish as a new species, Paretroplus dambabe, in 2002, he explicitly noted that it 'has been erroneously associated' with petiti 'for decades.' Sparks's 2008 revision of the genus retained petiti as a nominally valid species but flagged that it might in fact be conspecific with the pinstripe damba Paretroplus menarambo — a question that cannot be settled without fresh material. Much of the older aquarium and hobby literature describing 'Paretroplus petiti' from Lake Kinkony is therefore, in modern terms, an account of Paretroplus dambabe.
Morphology
Because Paretroplus petiti is known only from a single juvenile, its adult appearance is genuinely undescribed. FishBase records a maximum length of 4.5 in SL — essentially the size of the holotype, not a mature fish — and the species would be expected to grow far larger, like its damba relatives, which run from roughly 10–14 in. Pellegrin's specimen and Sparks's re-examination give the diagnostic outline: a deep, disk-shaped body, with body depth around 58% of standard length, placing petiti among the deepest-bodied members of the genus. Meristics from the holotype are 17 dorsal spines and 14 dorsal soft rays, with 9 anal spines and 14 anal soft rays — the high spine count of the anal fin (seven or more, versus three in all other native Malagasy cichlids) is a hallmark of Paretroplus. In preservation the fish is dark brown and lacks the bold lateral barring typical of the genus, a combination shared only with Paretroplus menarambo; it is told from menarambo by the absence of that species' fine 'pinstripe' pattern of spots on the scales. Like other dambas it carries lateral ridges of scales that stand free of the fin membranes along the entire soft dorsal and anal fins. Live coloration, adult proportions, and any sexual dimorphism are simply unknown — no living kotso has been studied. By analogy with the rest of the genus it would have a curved forehead, a small mouth, robust molar-like pharyngeal teeth, and a deeply forked, crescent-shaped tail.
Habitat
Paretroplus petiti is endemic to the freshwater lowlands of northwestern Madagascar, and Eschmeyer's Catalog of Fishes gives its distribution simply as 'Northwestern Madagascar.' The type came from the Maintimaso River, a small watercourse in the lower Betsiboka–Mahavavy region near the Mozambique Channel coast; some authors have suggested the original specimen may instead have come from Lake Ambanja in the same Betsiboka drainage, reflecting how poorly the collection was documented. Whatever its exact origin, the species belongs to the estuarine-influenced floodplain country of the northwest, a landscape of warm, turbid rivers, oxbow lakes, and seasonally flooded wetlands draining toward the sea. The IUCN classifies its habitat as inland wetlands. The dambas as a group occupy lakes, river pools, and shallow rivers over silt, sand, mud, or rock, in water that is usually soft but chemically variable — ranging from mildly acidic blackwater to distinctly alkaline (pH around 6.5 to over 8), and frequently very warm, often exceeding 86 °F. Several northwestern Paretroplus tolerate brackish-tinged water near the coast, and the lower-Betsiboka setting of petiti is consistent with that estuarine influence. No in-situ chemistry has ever been measured for the kotso itself; the figures here are the documented envelope for the genus in this region, applied for want of species-specific data.
Feeding
Nothing is recorded about the diet of Paretroplus petiti directly — there are no gut-content studies of a fish that has not been collected in nearly a century. Its trophic ecology can only be inferred from the genus. Paretroplus possess robust, molariform pharyngeal dentition, the crushing apparatus of a mollusc specialist: radiographs of the related Paretroplus maromandia show guts packed with crushed gastropod shells, and it is assumed that snails and other hard-shelled invertebrates form a significant part of most species' diets. They are not strict specialists, however — Paretroplus also graze algae and take a range of benthic foods, and the subfamily as a whole (apart from the herbivorous Etroplus suratensis) is fundamentally omnivorous. FishBase estimates a trophic level near 2.9 for petiti, consistent with an omnivore that works the bottom for invertebrates and plant material. In its floodplain habitat the kotso would have functioned as a deep-bodied benthic forager, using molar-like throat teeth to process snails and detritus from soft and rocky substrates.
Mating
The reproductive behaviour of Paretroplus petiti has never been observed; the species has never been kept in captivity and has not been studied alive in the wild. What is known applies to the genus. Paretroplus are monogamous, biparental fish that form pairs and defend a territory around a chosen spawning site. Across the genus the dambas — the deep-bodied lake and river-pool species to which petiti belongs — pair off and court over open substrate such as a rock or a piece of waterlogged wood, excavating a shallow depression rather than digging the deep tunnels of some Neotropical eartheaters. Field reports from local fishermen place the breeding season of Malagasy dambas in the latter part of the dry season, roughly August through October. Like many large substrate-spawning cichlids these are robust, sometimes aggressive fish that establish and hold territory vigorously through the pairing and spawning period. Whether the kotso differs in any of these respects is unknown and, given its possible extinction, may never be learned.
Breeding
No spawning of Paretroplus petiti has ever been recorded — not in the wild and not in aquaria, since the fish has never been brought into captivity. The account here is genus-typical, drawn from its damba relatives. Paretroplus are biparental open-substrate spawners: a pair cleans a site (a rock, sunken wood, or in tanks a flowerpot or a bare patch of bottom) and the female deposits a clutch of large, adhesive, salmon-orange eggs, which both parents then guard and tend through hatching and the free-swimming fry stage, in the manner of the substrate-spawning cichlids of the Americas. Clutch sizes for the deep-bodied dambas are typically on the order of a few hundred eggs. The dambas spawn in the late dry season (about August–October). Fry are slow-growing but reach maturity relatively young for cichlids, around 12 to 18 months; breeders of related species stress that the young must be reared on live food, such as Artemia nauplii, for the first several months. For the kotso specifically, every one of these details is an inference — its true clutch size, egg colour, parental roles, and developmental timing are all unknown.
In the aquarium
Paretroplus petiti has never been kept in the aquarium hobby. Unlike several of its relatives — which were collected in northwestern Madagascar from the early 1990s by Jean-Claude Nourissat, Patrick de Rham, and Laif Demason, then bred in outdoor ponds and tanks in France, the United States, and at the Bolton Museum Aquarium in England — the kotso was never exported and, as far as the record shows, has not been seen alive by any aquarist or ichthyologist since its single specimen was taken. There is therefore no genuine husbandry experience to report for this species, and any 'care guide' purporting to describe keeping 'Paretroplus petiti' is almost certainly describing the Lake Kinkony fish now known as Paretroplus dambabe, which was kept and bred under the petiti name for years. If the kotso still exists and were ever collected, it would demand what the other dambas require: a large aquarium (the smaller Paretroplus need at least ~105 US gal, the larger ones 185 US gal or more), a fine sand substrate with rock and wood, well-filtered water changed frequently, and a near-neutral to alkaline pH kept warm — above about 75 °F for maintenance and warmer still for any breeding attempt. These are social but robust and at times aggressive fish best held in a group to spread tension, and as confirmed mollusc-eaters they relish snails alongside quality prepared and frozen foods. All of that, however, is borrowed from its congeners; for Paretroplus petiti itself it remains hypothetical.
Conservation
The IUCN Red List assesses Paretroplus petiti as Data Deficient, assessed and published in 2016 by Ravelomanana and Sparks, with an unknown population trend. The Data Deficient rating reflects the species' near-total obscurity: it is known from a single juvenile collected almost a century ago, its precise type locality is uncertain, and its validity as a species distinct from Paretroplus menarambo is itself in question — there is simply not enough information to judge its status against the threatened categories. The assessment lists logging and wood harvesting among the pressures on its presumed range. That uncertainty sits within a genus in crisis. Madagascar's Paretroplus are among the most imperilled cichlids anywhere: several congeners — P. maculatus, Paretroplus menarambo, Paretroplus dambabe, and Paretroplus gymnopreopercularis — are listed Critically Endangered, and Paretroplus menarambo is feared extinct in the wild. The drivers are habitat degradation across the northwestern floodplains, the introduction of non-native tilapia and snakeheads, and overfishing of fish that were once a prized local food. Some species survive only through captive-breeding programs maintained by dedicated aquarists and public aquaria. The kotso has no such lifeline: with no living specimen in any collection, if it is a valid species it may already be lost — a reminder that some of Madagascar's endemic cichlids could vanish before they are ever properly known.