Taxonomy & naming
The Teapa cichlid was described by the Austrian ichthyologist Franz Steindachner in 1864, on material from the Río Teapa in Tabasco, southern Mexico — a tributary system within the great Grijalva drainage. The epithet gibbiceps, from Latin gibbus (hump) and -ceps (head), refers to the hunchbacked forehead of some adults. Like nearly all Mexican river cichlids the species spent the twentieth century lodged in the vast wastebasket genus Cichlasoma, and it has at times been placed in Vieja and Theraps as those genera were variously circumscribed. Charles Tate Regan's genus Paraneetroplus (type species Paraneetroplus bulleri) was resurrected and restricted by the molecular revisions of McMahan, Matamoros, Piller & Chakrabarty (2015, Zootaxa 3999) and Říčan, Piálek, Dragová & Novák (2016), which recovered gibbiceps among the close relatives of bulleri — the elongate, flowing-water 'lotic' grade of the herichthyine radiation. The species sits at the centre of a small nomenclatural tangle: the name Paraneetroplus omonti Allgayer, 1988 is recognised as a distinct species by Eschmeyer's Catalog of Fishes but treated by FishBase as a junior synonym of Paraneetroplus gibbiceps, so depending on the authority the Teapa cichlid is one species or two.
Morphology
Paraneetroplus gibbiceps is a medium-large, elongate and laterally compressed cichlid of the streamlined riverine type, reaching about 9 in standard length per FishBase. The ground colour is silvery to olive with a greenish or bluish iridescent cast over the flanks, overlaid with a variable pattern of darker vertical bars or a broken mid-lateral band that strengthen with mood and breeding condition. The genus's namesake feature is most pronounced here: mature, dominant fish — especially large males — build a steep, bulging forehead and nuchal region, the 'humped head' the epithet records. The mouth carries the comb-like, slightly spatulate teeth typical of the genus's algae-scraping habit. Sexual dimorphism follows the heroine pattern: males grow larger and develop the steeper forehead and the heaviest nuchal swelling, while ripe females are deeper-bellied and drop a visible ovipositor when spawning. As with most narrow-range Mexican cichlids, much of the detailed morphological record rests on preserved museum specimens rather than systematic study of living fish.
Habitat
The species occurs on the Atlantic (Gulf of Mexico) slope of southern Mexico, in the Usumacinta and adjacent Grijalva river basins, with its type locality on the Río Teapa in Tabasco. These are warm lowland-to-foothill rivers draining the Petén-Veracruz moist forest and the flanks of the Chiapas highlands, and the genus's general preference is for flowing, well-oxygenated reaches over rock and gravel rather than still backwaters. FishBase classes the fish as freshwater and benthopelagic and gives a preferred temperature band of roughly 73–79 °F. The Grijalva–Usumacinta system is one of the most fish-rich and most heavily endemic drainages of Middle America, and it is recognised as its own Freshwater Ecoregion of the World. Quantitative in-situ chemistry and a published depth range specific to this species are sparse, as is typical for the region's river cichlids; the figures here lean on FishBase's environmental envelope and the general character of the drainage rather than a dedicated field-limnology study.
Feeding
FishBase places Paraneetroplus gibbiceps a little higher on the food web than its strict-grazer congeners, with a trophic level near 3.3, reflecting an omnivorous habit estimated from its size and closest relatives rather than a published gut-content study. In practice the genus works hard surfaces and the substrate with its comb-like teeth, scraping algae and aufwuchs and combing the bottom for the small invertebrates that come with it — a generalist bottom-oriented forager of flowing-water reaches. The mix of plant, detrital and small-animal food typical of the genus places it among the bottom-working omnivores of the Grijalva–Usumacinta rivers rather than among dedicated piscivores. As with its relatives, the bulk of its intake in the wild is low-energy grazed material, which shapes both its gut and the patient, near-continuous way it feeds.
Mating
Reproduction in Paraneetroplus gibbiceps, as in most large heroine cichlids, is organised around a monogamous pair that bonds and then jointly holds and defends a territory. Detailed field observations of courtship in this species have not been published, so the account is built from the genus's biology and from aquarium experience with its relatives. Pairs form within a group as fish mature; courtship runs through the familiar cichlid sequence of lateral displays, fin-spreading, jaw-locking and substrate cleaning, the female deepening in colour and dropping her ovipositor as she ripens. In a flowing-water cichlid of this build a defensible hard surface in or beside the current typically anchors the pair's territory, and intraspecific aggression rises as the territory is claimed and held. The reliable route to a compatible pair in captivity is to grow a cohort together and let a bond form rather than to force two adults into proximity.
Breeding
Paraneetroplus gibbiceps is a biparental substrate (open) spawner, the standard mode for its genus. The pair selects and meticulously cleans a hard surface — a flat rock, a slab of wood, the wall of a crevice — and the female lays an adhesive sheet of eggs over it while the male follows to fertilise. A precise wild clutch count has not been published for the species; cichlids of this body size typically lay on the order of several hundred eggs, and a productive pair can be expected to fall in that range. Both parents share the brood: the female fans and tends the eggs while the male patrols and defends the perimeter, and after the eggs hatch the wrigglers are moved to pre-dug pits before the free-swimming fry are shepherded as a tight school by both adults. The young feed initially on fine prepared foods and the aufwuchs the adults graze. Systematic captive-breeding accounts are scarce for this narrow-range species, which is far less often kept than the popular larger 'Vieja'.
In the aquarium
Paraneetroplus gibbiceps is a fish for the experienced large-cichlid keeper rather than the beginner — not because it is delicate, but because of its eventual size, its preference for flowing well-oxygenated water, and the management that big heroine cichlids demand. A foot-long riverine grazer needs real volume and flow: a single adult or a pair is best in a tank of at least 75 US gallons (roughly 75 US gal), and a longer footprint with strong circulation makes managing the fish, and any tankmates, considerably easier. Temperature is best kept in the middle of the tropical range (about 75–81 °F) with vigorous, well-oxygenated flow rather than a still, warm tank.
Water should be near-neutral to mildly alkaline (about pH 7.0–8.0) and moderately hard, matching the mineral-rich rivers of the Grijalva–Usumacinta system; the fish is hardy across this range but, like all big cichlids, is intolerant of accumulated dissolved waste, so generous filtration and large regular water changes are essential. A substrate of sand or fine gravel with plenty of smooth water-worn rock suits its bottom-grazing, rock-scraping habits; like its relatives it will rearrange décor and uproot rooted plants, so robust or potted plants and rockwork that create broken sightlines and defensible territories are the sensible furnishings. Because the fish is naturally a bottom-working omnivore that grazes a great deal of aufwuchs, its diet should be built around quality vegetable- and spirulina-based prepared foods, supplemented with frozen or live items in moderation; an over-rich, exclusively meaty diet is a poor match for its biology.
Tankmates should be similarly sized, robust riverine cichlids and large, fast dither fish that can hold their own; very small or slow fish will be outcompeted or, during spawning, harassed. The species is territorial and becomes markedly more aggressive in breeding condition, so the proven approach is to grow a group of six or more juveniles together to allow a natural pair to form and to spread aggression. It is an uncommon fish in the trade, kept mainly by specialists in Mexican riverine cichlids.
Conservation
The IUCN Red List assesses Paraneetroplus gibbiceps as Data Deficient, in an assessment dated 18 September 2018. The Data Deficient listing reflects exactly what its biology suggests: a fish of the Grijalva–Usumacinta rivers for which there is not enough information on population size, trend or specific threats — compounded by the unresolved taxonomy around Paraneetroplus omonti — to place it confidently in a threatened or non-threatened category. It carries no CITES listing. The Grijalva–Usumacinta system, though large and fish-rich, faces intensifying pressures across its lowland reaches: damming (the Grijalva is one of the most heavily dammed rivers in Mexico), pollution, deforestation in the catchment, water extraction, and introduced species. None of these is documented as a population-level threat to this particular cichlid, but for a Data Deficient river cichlid the appropriate posture is caution and a call for the basic distribution, taxonomic and population work the Red List flags as missing.