Taxonomy & naming
Teleocichla proselytus was described by the Swedish ichthyologist Sven O. Kullander in 1988, in the same monograph (Copeia 1988, no. 1: 196–230) in which he erected the genus Teleocichla itself for a suite of six new rheophilic species from the rapids of the Rios Xingu, Tapajós and Tocantins. The holotype (MZUSP 33065) and its paratypes were collected in the Rio Tapajós drainage in Pará State, Brazil — at São Luis, near Itaituba, where two of the type localities lay; Teleocichla prionogenys was described from the same river. Kullander coined the genus name to flag a striking case of convergent evolution: the elongate, worm-like body and continuous lateral line of these South American fishes parallel the African rapids genus Teleogramma, while the suffix -cichla signals their true phyletic place beside the pike cichlids, Crenicichla. That kinship is more than skin-deep; the catalogue history of this very species records a stint when Anthony Ploeg (1991) and others treated it as Crenicichla proselytus before it was returned to Teleocichla, and the genus is consistently recovered as a small, mouth-modified offshoot of the crenicichline lineage. The species remains valid as Teleocichla proselytus Kullander 1988, in family Cichlidae, subfamily Cichlinae. The genus has since grown well beyond its original six: Zuanon & Sazima added Teleocichla centisquama in 2002, Varella and colleagues described Teleocichla preta (2016) from the Xingu and Teleocichla wajapi (2013) from Amapá, and several forms remain undescribed — Kullander himself noted as early as 1990 that at least four more awaited names.
Morphology
This is a small, drably coloured fish. The largest type specimen Kullander measured was 2 in in standard length, and even the bulkiest congeners rarely exceed three inches; gravid females of related species mature below 2 in. The body is elongate and slightly tapered, with only moderate lateral compression, a short down-turned snout, and the small inferior mouth that is the genus' defining feature — not the wide gape of a predatory pike but a modest terminal-to-subterminal mouth suited to picking tiny invertebrates from rock, often likened to the mouth of a marine dragonet (Callionymidae). Two further adaptations betray the rapids habit: a reduced swim bladder that denies the fish neutral buoyancy and keeps it on the substrate, and long, relatively stiff pelvic fins with a thickened outer margin. Several Teleocichla are known to splay their pectoral fins horizontally like aeroplane wings in current so that the rushing water presses them down onto the rock — a living suction strategy. Coloration is muted and cryptic, a grey-brown ground that matches stone, although aquarium specimens of Teleocichla proselytus show attractive orange in the fins. As the epithet implies, the species is diagnostically nondescript: Kullander named it the "stranger" precisely because it lacks the bold lateral-line or barring characters that separate its better-marked relatives. Sexual dimorphism is poorly documented; as in congeners, ripe females are deeper-bodied and males tend to run slightly larger with more developed fins.
Habitat
Teleocichla proselytus is endemic to the Rio Tapajós drainage of the lower Amazon basin in Brazil, recorded from São Luis near Itaituba and, on the basis of the type series, from a second locality on the same river. The whole genus is tied to a single broad biotope — the rocky rapids and rapids-bed streams of the clearwater rivers draining the Brazilian Shield — and, despite being well adapted to fast water, Teleocichla in general seem to avoid the small rivulets that feed the main channel. But field observation of Teleocichla proselytus specifically (Konings, Enjoying Cichlids) found the species in the Tapajós not only in the rocky rapids proper but also over open sand in shallow water near sandy beaches, a broader habitat use than the 'rapids obligate' picture the genus is usually given. These are not the soft black or turbid white waters of the Amazon lowlands but transparent, fast, oxygen-rich highland rivers running over bare rock. Field chemistry for the genus, measured by Rainer Stawikowski and colleagues at Altamira on the neighbouring Rio Xingu, gives the texture of the environment: pH around 6.5, general and carbonate hardness each below 1 °dH, conductivity near 120 µS/cm, and water temperatures that climbed to about 90 °F in the September low-water season. The fish were found over rocky bottom in roughly a metre of water in the main river channel, where adult males hold small territories around individual stones, pits, and holes, darting under flat rocks when threatened. FishBase records a comparable envelope for Teleocichla proselytus specifically — pH from about 5.5 upward, hardness to 1 °dH, and a tropical range of 81–91 °F — confirming a soft, warm, slightly acidic-to-neutral clearwater fish of shallow, swift, stony habitat. A documented captive breeding setup matched this profile closely: about 150 µS/cm conductivity, pH 6.3 and 82 °F.
Feeding
Despite its membership in the pike-cichlid lineage, Teleocichla is not an ambush predator. The whole point of the genus, as Kullander and later Stawikowski stressed, is the reduced mouth: where Crenicichla swallows prey whole, Teleocichla picks. The small inferior mouth and fine dentition equip Teleocichla proselytus to graze tiny invertebrates — aufwuchs fauna, insect larvae, and other micro-organisms — from the surfaces of rocks in the current, a micropredator working the interstitial film of the rapids rather than hunting open water. FishBase places it at a trophic level near 3.1, consistent with an invertebrate-picking carnivore. This trophic shift is thought to be the key to the genus' success: by exploiting a feeding niche no other cichlid in the rapids could reach, Teleocichla radiated into a small species flock in rivers already occupied by rheophilic Crenicichla without competing head-to-head with them. In aquaria the diet translates straightforwardly into small frozen and live fare — bloodworm, daphnia, and brine shrimp are taken readily, with some individuals accepting flake.
Mating
Reproductive behaviour in the wild has not been described in detail for Teleocichla proselytus, and Kullander himself noted that no particular observations of Teleocichla in their natural habitat had been made at the time of the genus description. Aquarium observation (Konings, Enjoying Cichlids) fills in some of the social picture: Teleocichla, including this species, are essentially solitary and show a marked tendency to chase other fish, predominantly their own kind — but that aggression is milder than the genus' pike-cichlid ancestry might suggest, restricted to short chases after which the dominated fish is simply left alone rather than pursued to injury. Adult females are able to dominate larger males, an unusual reversal for a cichlid. What is known of the genus more broadly points to a territorial, substrate-bound social system: adult males defend small territories anchored on a stone, a crevice, or a hole in the rock, and species differ markedly in how sociable or aggressive they are. Remarkably, the rapids can pack several Teleocichla species into the same few square metres: Stawikowski reported finding three different species sheltering under a single rock on the Xingu, which implies strong behavioural — rather than spatial — barriers to interbreeding. In a documented breeding group, a single male held territory with three similarly sized females, each of whom in turn held her own individual territory and nest, rather than the male and one female forming an exclusive bonded pair; courtship in that setting is best understood as the male cycling between several resident, competing females rather than classic one-on-one pair formation.
Breeding
Wild spawning of Teleocichla proselytus has not been described, but the species has in fact been bred and documented in captivity, in a harem setup reported in Konings' Enjoying Cichlids — corrected here from an earlier assumption that its breeding was essentially unrecorded. One male was kept with three same-sized females in a 100 × 60 × 15.5 in tank floored with 2 in of sand and pebbles topped with flat stones, filtered by a sponge filter turning over about 800 l/hr, at roughly 150 µS/cm conductivity, pH 6.3 and 82 °F. Each female excavated her own nest under a stone at the centre of an individually held territory, and the male spawned with each female in turn, 2–3 weeks apart. Notably, no strong pair bond of the kind normally seen in Crenicichla — the genus' closest relative — was observed; this is a harem-spawning, not a pair-bonding, species, at least under these conditions, and parental care should be read with that caveat rather than assumed to be classically biparental. Egg number, egg size and incubation period varied between females. Eggs took about two weeks to hatch and release free-swimming fry — roughly six days longer than in dwarf Crenicichla — and the fry themselves, at about 0.5 in on emergence, behaved noticeably more independently than dwarf-Crenicichla fry, needing less active shepherding. First spawns from a given female produced around 30 fry; later spawns from the same females numbered only 5–10. Fry took Artemia nauplii without difficulty. After roughly three to four weeks, a female begins driving her fry away from the nest site as she prepares to spawn again. Beyond this one documented account, reliable captive reproduction of the species remains scarce, and any figures beyond those given here (for clutch structure, for instance, rather than fry counts) should still be treated as inferred from congeners.
In the aquarium
Teleocichla proselytus is a specialist's fish, only occasionally imported and demanding to keep well. It ships poorly — exporters have historically refused to guarantee live arrival of Teleocichla, and the fish do not tolerate the slow, still water of a typical transport bag or a non-rheophilic tank; early American attempts to keep imported congeners ended in near-total loss within days. Anyone serious about the species should plan to recreate the rapids, and should size the tank for a small harem rather than a single pair: a documented breeding group of one male with three females was kept successfully in a 100 × 60 × 15.5 in (roughly 200 l) tank, and that footprint is a reasonable working minimum, larger being better still. The priorities are strong, well-oxygenated current and a stony floor: worn river pebbles and rounded rock piled into caves, crevices, and overhangs give the fish the holes they instinctively claim and hide in, and a substrate of mixed sand and pebbles a few centimetres deep, topped with flat stones, lets territorial females excavate nests the way they do in a documented breeding setup. A powerhead or river-style return to drive brisk flow is more important than tank volume, and high oxygen saturation is non-negotiable for a fish from cool, turbulent, oxygen-rich water — though the source rivers run warm, so a temperature in the high 20s °C (around 81–86 °F) suits it.
Water should be soft and clean, slightly acidic to neutral (roughly pH 6.0–7.0), low in hardness, and impeccably maintained; these are fish of pristine, fast water and they will not forgive accumulated waste or low dissolved oxygen. Because the swim bladder is reduced, the fish rests and "hops" along the bottom rather than hovering, so usable floor area and abundant ground-level shelter matter more than height. Feeding is straightforward once the fish are settled: small frozen and live foods — bloodworm, daphnia, brine shrimp — are taken eagerly, mimicking the rock-picked invertebrate diet of the wild; a documented captive breeding group was raised on Artemia nauplii as fry food.
Temperament is milder than the pike-cichlid lineage might suggest. Observed aggression in Teleocichla, this species included, is largely solitary chasing rather than sustained fighting — a dominated fish is chased off and then simply left alone, not pursued to injury — and adult females can dominate larger males. Teleocichla proselytus in particular tolerates being kept in small groups (unlike strongly territorial congeners such as T. gephyrogramma and T. monogramma, which need to be kept strictly as pairs), which makes a one-male, multi-female harem a workable and, per the documented account above, breeding-productive approach. The one hard rule for tankmates, of any kind, is that only species not competing directly for the same territories can be housed with Teleocichla — current-tolerant fish that use a different part of the tank, such as small loricariid catfishes from the same rapids, are natural companions, and nothing should be large enough to bully or eat a six-centimetre bottom-dweller. This is not a community fish and not a beginner's fish; it rewards a keeper willing to build and maintain a dedicated rapids aquarium.
Conservation
The IUCN Red List assesses Teleocichla proselytus as Least Concern, in an assessment carried out in 2018 by Brazil's Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) with P. Reis and a large panel of Brazilian ichthyologists, published in 2022; the population trend is listed as unknown. The two threats flagged are mining and quarrying and, more significantly for a rapids endemic, dams and water management. That second pressure is the real concern for the genus. Teleocichla are obligate rapids fish whose entire world is the fast, rocky stretches of Shield-draining clearwater rivers — precisely the stretches targeted for hydroelectric development. The cautionary case is the congener Teleocichla cinderella, whose Rio Tocantins type locality near Tucuruí was destroyed outright by the Tucuruí dam, and the Tapajós basin that holds Teleocichla proselytus has itself been the subject of repeated large-dam proposals. A rheophilic species with a narrow range and a habitat that vanishes when a river is impounded is far more exposed than its Least Concern listing alone conveys, even where current population data are lacking. The species carries no CITES or CMS listing and is harmless to humans.