Taxonomy & naming
Cichlasoma sanctifranciscense was described by the Swedish ichthyologist Sven O. Kullander in 1983, in his monographic A Revision of the South American Cichlid Genus Cichlasoma, published by the Swedish Museum of Natural History. The type locality is Lagoa Viana, in the Rio São Francisco system of Bahia, Brazil; the holotype (NMW 32714) is held in the Naturhistorisches Museum in Vienna. The species is one of the great clarifying products of Kullander's revision. Before 1983, 'Cichlasoma' was a sprawling catch-all of roughly a hundred nominal species stretching across the Americas; Kullander restricted the genus to a small, monophyletic core of generalised South American acaras built around its type species Cichlasoma bimaculatum, and in doing so described seven new species — amazonarum, araguaiense, boliviense, orientale, orinocense, paranaense, pusillum and sanctifranciscense among them — each tied to a particular drainage. The roughly hundred Central American 'Cichlasoma' were turned out of the genus entirely and now sit in Amphilophus, Vieja, Herichthys, Thorichthys and their kin. Cichlasoma sanctifranciscense belongs to Cichlasoma sensu stricto, within the tribe Cichlasomatini of the Neotropical subfamily Cichlinae. The name has never been reassigned, and the Catalog of Fishes lists it as valid; no synonyms attach to it. The epithet is a straightforward toponym — 'of São Francisco' — for the river basin where the type material was collected.
Morphology
Cichlasoma sanctifranciscense is one of the smallest members of its genus, reaching only about 3.5 in in standard length (FishBase) — at the lower end of a genus whose species run from under 3 in to around 5 in. In build it is a typical small Cichlasoma acara: a moderately deep-bodied, laterally compressed cichlid with the generalised, unspecialised shape that the genus is known for, a terminal mouth and the rounded-to-pointed unpaired fins of a substrate-spawning cichlasomatine. The ground colour is a silvery to pale brownish base overlain by the dark markings characteristic of the genus — a longitudinal lateral stripe and a discrete spot at the caudal-fin base, with vertical trunk bars that can flush in with mood and condition. In Kullander's diagnosis the species is distinguished from its congeners by a suite of meristic and squamation characters; notably it carries a unisserial (single-row) predorsal scale pattern, in contrast to the trisserial predorsal squamation of the closely allied Cichlasoma orientale and Cichlasoma zarskei — a useful technical separator within this look-alike group. Detailed sexual dimorphism is not separately published for the species; on the genus pattern, males tend to grow a little larger with somewhat longer-pointed fins and ripe females are rounder-bodied, but for sanctifranciscense this should be read as the expected acara pattern rather than a documented account.
Habitat
Cichlasoma sanctifranciscense is a freshwater fish of eastern Brazil, with a range centred on two large drainages of the region: the Rio São Francisco and the Rio Parnaíba basins, with records also referred to the Capivara system. FishBase notes it as common from around Brasília east to the western side of the Chapada Diamantina — a span across the São Francisco's middle and upper reaches in the interior of Bahia, Minas Gerais and the central plateau. These are the warm, often seasonal waters of the Brazilian shield and the São Francisco valley: a major river system with its associated lagoons, backwaters and tributaries. FishBase classes the species as a benthopelagic tropical freshwater fish that inhabits rivers. As a small, generalised acara it is the kind of cichlid that does well in the slower, structured margins of these systems — lagoons such as its type-locality Lagoa Viana, backwaters and quieter river stretches — rather than in fast open channels. The bulk of its range lies in the São Francisco freshwater province, a drainage with a distinctive, partly endemic fish fauna.
Feeding
No dedicated diet study has been published for Cichlasoma sanctifranciscense; FishBase estimates a trophic level of about 3.0 from the species' size and the diets of its close relatives, placing it squarely in the omnivore band that characterises the genus. On the pattern of Cichlasoma and the wider cichlasomatine acaras, it is best understood as a generalist benthic feeder, taking small aquatic invertebrates — insect larvae and small crustaceans — together with detritus and some plant material from the substrate and the structured margins of its rivers and lagoons. Acaras of this kind work the bottom and the leaf litter, taking mouthfuls of sediment and sorting edible items, but they are flexible opportunists rather than specialists. In its riverine community sanctifranciscense sits in the middle of the food web, a small invertebrate-leaning omnivore that is itself prey for the larger predatory fishes of the São Francisco.
Mating
Reproductive behaviour has not been observed in detail for Cichlasoma sanctifranciscense, but the genus and the broader cichlasomatine acaras are highly uniform in their breeding biology, and the species can be expected to follow that template. These are pair-bonding, biparental substrate spawners. A male and female form a pair, select and clean a spawning surface — typically a flat stone or a cleared patch of firm substrate — and defend a territory around it together. Outside of breeding small Cichlasoma are relatively peaceable, loosely social fish, but a pair coming into condition becomes territorial around its chosen site. Courtship follows the familiar acara repertoire of mutual lateral displays, fin-spreading and quivering and trial passes over the cleaned surface before spawning. As in related acaras, pairs form most reliably when fish choose their own partners from a group rather than being forced together.
Breeding
On the genus-typical pattern, Cichlasoma sanctifranciscense is an open, biparental substrate spawner. The female lays adhesive eggs in rows on a cleaned hard surface, and both parents tend the brood through the standard cichlasomatine division of labour — the female staying close to mouth and fan the eggs, the male patrolling the perimeter and repelling intruders. After hatching the wrigglers are moved to one or more pits dug in the substrate, and once free-swimming the fry are herded and guarded as a school by both parents. Specific clutch counts for sanctifranciscense are not published; small Cichlasoma of this size lay on the order of a couple of hundred eggs per spawn. This biparental open-substrate strategy — eggs on a surface, larvae in a pit, a guarded free-swimming shoal — is the reliable acara pattern, and there is no published account of any departure from it in this species, whose breeding has simply not been documented in detail.
In the aquarium
Cichlasoma sanctifranciscense is essentially a wild Brazilian species rather than an aquarium fish; it is rare in the trade, and the keeping notes that follow are extrapolated from the genus, several members of which (notably Cichlasoma portalegrense and Cichlasoma dimerus) are familiar, easygoing aquarium acaras. As one of the smallest Cichlasoma, at under 3.5 in, it is a manageable cichlid — a pair would be comfortable in a tank of around 25–30 US gal or more, with a longer footprint helping a pair hold a territory at breeding time and letting a group sort out a pairing naturally.
Water should track its warm eastern-Brazilian rivers and lagoons: moderate, broadly neutral conditions suit a generalised acara from the São Francisco and Parnaíba, with stable, clean water and regular partial changes mattering more than precise chemistry. Aquascaping should echo the structured river-margin and lagoon habitat — a soft substrate the fish can dig in, driftwood and rockwork for cover and sightline breaks, and at least one flat stone as a potential spawning slate. Feeding is straightforward for an omnivore: a varied diet of small prepared foods alongside live and frozen invertebrates brings out the best condition and colour. On the genus's temperament, expect a comparatively peaceable fish away from spawning that becomes territorial around a nest; robust, similarly sized South American community fish make sensible companions, and raising a group together to let a pair form is the surest route to breeding. For now this remains far more a fish of the São Francisco than of the hobby.
Conservation
The IUCN Red List assesses Cichlasoma sanctifranciscense as Least Concern (assessed 7 November 2018). The species is distributed across two large eastern-Brazilian drainages — the São Francisco and Parnaíba — and is reported as common over much of that range, a reasonably wide and well-populated distribution for a small freshwater fish, which underpins the Least Concern listing. It carries no CITES listing and is of no fisheries interest. The broad pressures on eastern-Brazilian freshwaters form the backdrop against which its status should be read: the São Francisco in particular is a heavily modified river, subject to large dams, water abstraction for irrigation, pollution and the introduction of non-native species, all of which reshape the habitats of its native fishes. None of these is documented as a population-level threat to this particular cichlid at present, but as a fish of a much-altered major river system, its long-term outlook is tied to the broader condition of the São Francisco and Parnaíba basins.