Taxonomy & naming
Steindachner's cichlid was described by the American ichthyologists David Starr Jordan and John Otterbein Snyder in 1899 as Cichlasoma steindachneri, from the Tamasopo, Gallinas and Ojo Frío rivers of the Pánuco basin in San Luis Potosí, Mexico. The species passed through Cichlasoma and Herichthys before De la Maza-Benignos and colleagues, in their 2015 Hydrobiologia phylogeography, transferred it to their new genus Nosferatu — the molar-toothed 'labridens species group' of southern-Pánuco snail-eaters — named for the dark breeding bar these fish raise, after F. W. Murnau's 1922 silent-film vampire. As with the rest of the genus the split is contested, and FishBase and Eschmeyer's Catalog of Fishes retain the fish as Herichthys steindachneri, so the two names denote the same animal. The species was long confused with the much smaller, sympatric Nosferatu pame of the same upper-Gallinas waters; De la Maza-Benignos and Lozano-Vilano's 2013 work clarified the two, with steindachneri the large, more piscivorous form and pame the small white snail-eater. The name honours the Austrian ichthyologist Franz Steindachner, the prolific Vienna museum worker of the late nineteenth century.
Morphology
Herichthys steindachneri is the giant of its genus, reaching about 15.5 in in standard length — far larger than the 4.5–10 in of its relatives — with a correspondingly powerful build, a deep body and a large mouth. The lower pharyngeal plate carries the heavy pavement of rounded molariform teeth characteristic of the snail-crushing Nosferatu, but the larger mouth and more predatory habit set it apart from the smaller pure molluscivores. Outside of breeding it is a brassy-grey to olive fish, often with a row of dark mid-lateral markings and the dark caudal spot of the genus. In breeding condition it raises the bold dark vertical bar (or paired dark fields) for which the genus is named, against a paler, sometimes contrastingly marked body. Sexual dimorphism is modest, with males growing larger and heavier-headed; as in its relatives, venting gives the most reliable sex determination. Its size and predatory dentition make it the apex cichlid of its small native range.
Habitat
Steindachner's cichlid is a narrow-range endemic of the upper Río Gallinas–Tamasopo system in San Luis Potosí, on Mexico's Atlantic slope within the Pánuco basin, occurring in the Tamasopo, Gallinas and Ojo Frío rivers and their associated springs above the Tamul cascade. These are clear, hard, strongly alkaline headwaters — FishBase gives pH 7.8–8.3 and temperatures of about 73–84 °F — running over sand, gravel, rock and travertine, with stronger current than the still spring-lakes of the neighbouring Río Verde valley. It is a benthopelagic fish of the river channels and spring pools, ranging over the bottom and through the water column as a roving predator. It shares these waters with the small white snail-eater Nosferatu pame, the two partitioning resources by size and diet, and its distribution is sharply bounded by the geography of the upper Gallinas — beyond this single system it occurs nowhere else.
Feeding
Herichthys steindachneri is both a snail-crusher and a predator, the most carnivorous member of its genus. FishBase summarises its diet as snails and smaller fishes and places it at trophic level 4.0 — a top predator, markedly higher than the 3.3–3.4 of its molluscivore-omnivore relatives. Its heavy molariform pharyngeal mill crushes the hard-shelled gastropods of the upper Gallinas, while its large mouth and size let it take small fishes that the smaller members of the genus cannot. In its native streams it sits atop the cichlid food web, exploiting both the snail resource shared with Nosferatu pame and the small-fish prey base, and its predatory size is the trait that most clearly separates it from the otherwise similar snail-eaters of the Pánuco springs.
Mating
Steindachner's cichlid is a monogamous, pair-bonding substrate spawner. Pairs form as fish come into condition and become strongly territorial, claiming and defending a stretch of streambed around cover, with the dark breeding bar serving as a courtship and threat display. The thermally stable spring-fed headwaters allow pairs to come into breeding condition across much of the year. As in the tribe Herichthyini, both members of the pair hold the territory jointly; the female concentrates on direct egg and larval care while the male — large and powerful in this species — patrols and defends a sizeable perimeter against conspecifics and other fishes. Given the fish's size, breeding pairs command and defend correspondingly large territories.
Breeding
Herichthys steindachneri is a biparental substrate spawner. The pair cleans a firm surface — a rock face, a flat stone, or the wall of an excavated pit — and the female lays an adhesive clutch of ovoid eggs onto it; FishBase notes that the female tends mainly to the eggs and larvae. Both parents guard and fan the eggs and then escort the free-swimming fry in a school over the substrate, the powerful male defending the wider territory. As the largest member of its genus it produces correspondingly large clutches, and the stable spring environment permits reproduction across much of the year. It is an egg-layer that has been kept and bred by specialists, though its eventual size makes it a demanding fish to raise to and through breeding.
In the aquarium
Steindachner's cichlid is a large, demanding fish kept only by dedicated Central American cichlid specialists, both for its size and for its status as a threatened single-system endemic. Because it can approach 15.5 in, it needs a very large aquarium — a single adult pair really wants something on the order of 160 US gal or more (in the range of 150 US gallons and up), longer rather than taller, with a sand bottom, robust rockwork and wood, and the open swimming space a large, active predator requires. Powerful filtration and good oxygenation are essential to reproduce its clear, flowing spring-stream habitat and to handle the waste load of a big, meat-eating fish.
Water chemistry must reflect its hard, alkaline origins: pH well above neutral (its wild waters run 7.8–8.3) with high hardness, and a temperature in the mid-20s °C. Soft, acidic water is wrong for it. Diet should honour its predatory, snail-crushing nature — a carnivorous menu of quality prepared and frozen foods, with snails offered both as natural prey and to exercise the pharyngeal mill. Tankmates are a real challenge: only large, robust Central or North American cichlids can coexist with an adult, and even then a spawning pair becomes formidably aggressive; small fish are simply prey. This is emphatically not a community fish and not a beginner's fish — it is a large, powerful, space-hungry predator whose husbandry is closer to that of a managuense or a Nandopsis than to the small spring cichlids it is related to.
Conservation
Herichthys steindachneri is assessed by the IUCN Red List as Endangered (criteria B1ab(iii)+2ab(iii); assessed 19 October 2018), on the basis of its very small range — confined to the upper Tamasopo–Gallinas system above the Tamul cascade — and a declining, increasingly fragmented area of occupancy. In Mexico it is additionally covered by the official norm NOM-059-SEMARNAT. The pressures the assessors identify are those of a single-system spring-stream endemic: water extraction and diversion for agriculture, dam and impoundment effects, tourism and recreational pressure on the spring systems (the Tamasopo and Tamul areas are heavily visited), pollution from domestic and agricultural runoff, and the spread of introduced and translocated fishes through the Pánuco headwaters. As the apex cichlid of its tiny range — and a fish of some local fishery and aquarium-trade value, which adds collecting pressure — it is exposed to any degradation of the upper Gallinas, and its long-term survival depends on the protection of those headwater springs and streams.