Taxonomy & naming
The Sarabia cichlid was described by the British ichthyologist Charles Tate Regan in 1905 as Paraneetroplus bulleri, and it is the type species of the genus Paraneetroplus. Regan coined the genus name to mark a fish that seemed intermediate between Neetroplus and the deep-bodied 'mojarra' cichlids, sharing the chisel-like tooth row of Neetroplus on a more elongate body — para- ('near' or 'beside') prefixed to Neetroplus. For most of the twentieth century the wider assemblage of Mexican river cichlids was lumped into the vast wastebasket genus Cichlasoma, and Paraneetroplus itself was at various times treated as a synonym of or merged with Vieja and Theraps. The molecular revision of the herichthyine cichlids by McMahan, Matamoros, Piller & Chakrabarty (2015, Zootaxa 3999) — and the comprehensive phylogeny of Říčan, Piálek, Dragová & Novák (2016) — restricted Paraneetroplus to bulleri and its closest relatives (gibbiceps, nebuliferus, and the disputed omonti), all elongate 'lotic' (flowing-water) cichlids. The species epithet honours Audley Cecil Buller (1853–1894), a collector of Mexican vertebrates whose material includes the type specimen; the common name, by contrast, points to the type locality, the Río de Sarabia — a Coatzacoalcos tributary in northern Oaxaca.
Morphology
Paraneetroplus bulleri is a moderately large, elongate and laterally compressed cichlid built on the streamlined 'lotic' plan of its genus — a slim, muscular body suited to holding station in current rather than the tall slab-sided form of its still-water relatives. FishBase gives a maximum of about 10 in standard length, making it one of the larger members of the genus; with the tail a big male is roughly a foot long. Regan's 1905 original description cites a total length near 14 in, and at least one field naturalist reported specimens in the Isthmus that appeared to run larger still, though no confirmed measurement beyond that figure has been published — a discrepancy consistent with SL-versus-TL reporting but worth flagging rather than resolving here. The ground colour is a silvery to olive-grey, often with a green or bluish iridescent sheen over the flanks and a variable series of darker vertical bars or a broken mid-lateral stripe that intensify with mood and breeding condition; in life the fish is also described as carrying a dark horizontal stripe running the length of the body, its most conspicuous field mark. The head is comparatively pointed and the mouth set with the spatulate, comb-like teeth that Regan saw as Neetroplus-like, an adaptation for scraping. The tail fin is notably large and powerful for the fish's size, a build suited to swimming and holding station in current rather than to burst speed. Sexual dimorphism follows the heroine-cichlid pattern: males grow larger, develop a steeper forehead and, in old dominant fish, a modest nuchal hump, while ripe females are deeper-bellied and drop a visible ovipositor when spawning. Published in-life detail for this single-drainage endemic is thinner than for the popular aquarium 'Vieja', and much of the morphological record rests on preserved museum material.
Habitat
The species is endemic to the Atlantic (Gulf of Mexico) slope of southern Mexico, restricted to the Río Coatzacoalcos drainage at the northern end of the Isthmus of Tehuantepec — the narrow neck of land where the Gulf and Pacific come closest. It is a fish of the fast-flowing, well-oxygenated montane and foothill reaches rather than the sluggish lowland river, holding in riffles and runs over rock and gravel. FishBase classes it as freshwater and benthopelagic and gives a preferred temperature band of roughly 73–77 °F, on the cooler side of the tropical range, consistent with upland clear-water streams; reported water is near-neutral to alkaline (pH around 7.5 and up). A field account by Ad Konings (Cichlids Yearbook) of a typical Isthmus river gives a concrete picture of this habitat: a channel roughly 33 ft wide with about as much exposed riverbed between the banks, flowing at a moderate pace over a fairly steep gradient, its bed strewn with boulders and running around 3 ft deep with pools to about 7 ft, the pools themselves floored in mud to sand. Local fishermen around the Río Coatzacoalcos know Paraneetroplus bulleri as the "Corrientera" — the current fish — for its habit of holding station in fast water; the same name and the same river-current build turn up in a closely related, ecologically equivalent Paraneetroplus population Konings observed in the neighbouring Río Papaloapan drainage, though that population is a separate, undescribed lookalike rather than confirmed P. bulleri, and is not treated here as part of this species' documented range. The Coatzacoalcos is one of the Freshwater Ecoregions of the World units noted for a high proportion of strictly local fishes, and Paraneetroplus bulleri is among the endemics that define it. A quantitative depth range specific to this species is otherwise sparse, as is typical for the narrowly distributed Mexican 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
Paraneetroplus bulleri is a grazer low on the food web. FishBase assigns it a trophic level near 2.0 and records its diet as algae and aufwuchs — the carpet of algae, biofilm, detritus and associated micro-invertebrates that coats submerged rock in flowing water. This fits the elongate, current-adapted body and the chisel-like teeth: the fish works hard surfaces in the riffles, scraping and combing the algal turf and taking whatever small animal life comes with it. Among the Paraneetroplus this rheophilic grazing habit is the rule, and it places the Sarabia cichlid in the same functional guild as many of the rock-scraping cichlids of fast Central American rivers. Because so much of its energy comes from bulky, fibre-rich plant and detrital matter, it has the long gut and the patient, near-continuous feeding style of a herbivore rather than the lunge-and-gulp habit of a predator — a distinction that matters in captivity, where an over-rich, protein-heavy diet does not suit it.
Mating
As with most large heroine cichlids, reproduction in Paraneetroplus bulleri is organised around a monogamous pair that forms a bond and jointly holds and defends a territory. Detailed field observations of courtship in this particular species have not been published, so the picture is assembled from the genus's biology and from aquarium experience with its close relatives. Pairs form within a group as fish mature; courtship runs through the usual cichlid repertoire of lateral displays, fin-spreading, jaw-locking and substrate cleaning, with both sexes intensifying in colour and the female dropping her ovipositor as she ripens. In flowing-water cichlids of this build, a defensible hard surface in or beside the current — a rock face, a crevice, an undercut — typically anchors the territory. Intraspecific aggression flares as a pair claims its patch, and the practical route to a compatible pair, in the aquarium, is to raise a cohort together and let a bond develop rather than to force two adults into proximity.
Breeding
Paraneetroplus bulleri is a biparental substrate (open) spawner, the standard mode for its genus and for the elongate Middle American river cichlids generally. 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. As with many narrow-range Mexican endemics, captive breeding reports are scattered rather than systematic, and the species is far less often spawned than the popular larger 'Vieja'.
In the aquarium
Paraneetroplus bulleri is a fish for the experienced keeper of large riverine cichlids rather than a beginner — not because it is delicate, but because of its eventual size, its preference for cool, fast, clean water, and the management that big heroine cichlids demand. A foot-long, current-loving 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, well-oxygenated circulation makes managing the fish, and any tankmates, considerably easier. Unlike the warm-lowland 'Vieja', this is a fish of cooler upland streams, so the temperature is best kept toward the lower tropical range (about 73–79 °F) with vigorous 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 clear streams of the Coatzacoalcos; 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 herbivore-detritivore grazing aufwuchs, its diet should be built around quality vegetable- and spirulina-based prepared foods, supplemented sparingly with frozen or live items; an over-rich, meat-heavy diet is a poor match for its biology and is implicated in the bloat that plagues over-fed Central American grazers.
Tankmates should be similarly sized, robust riverine cichlids and large, fast dither fish that can hold their own in current; 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, both to allow a natural pair to form and to spread aggression. Given space, cool clean flowing water, a vegetable-leaning diet and time, it is a handsome and characterful aquarium fish; it is, however, rarely traded outside specialist circles and is far less familiar than the big-box 'Vieja' it superficially resembles.
Conservation
The IUCN Red List assesses Paraneetroplus bulleri as Least Concern, in an assessment dated 1 March 2018. The Least Concern listing reflects a species that, while restricted to a single drainage, is reasonably widespread and apparently stable within the Coatzacoalcos basin and faces no documented basin-wide threat severe enough to qualify it for a threatened category. It carries no CITES listing. That said, single-drainage endemism is itself the heart of the long-term concern: a fish confined to the Coatzacoalcos has nowhere else to go, and the basin is a heavily industrialised lowland region subject to the familiar pressures on Mexican Atlantic-slope rivers — habitat alteration, pollution, deforestation in the catchment, water extraction, and introduced species. As a flowing-water specialist of the cooler upland reaches it is also exposed to anything that alters flow or warms and silts its streams. None of these is documented as a present population-level threat to this particular cichlid, but they are the backdrop against which the status of any narrow-range Isthmus endemic should be read.