Taxonomy & naming
Amphilophus supercilius was described by Matthias F. Geiger, Jeffrey K. McCrary and Jay R. Stauffer Jr. in 2010, in the Proceedings of the Biological Society of Washington (123(2):159–173; DOI 10.2988/09-20.1). The same paper erected two new Midas cichlids from Lake Apoyo — supercilius and the globe-bodied Amphilophus globosus. The Catalog of Fishes and FishBase both carry it as a valid species with no synonyms, and the name is registered in ZooBank. Genus Amphilophus sits in the Neotropical cichlid subfamily Cichlinae (placed by some authors in Cichlasomatinae / tribe Heroini), and within it supercilius belongs to the Amphilophus citrinellus species complex — the "Midas" cichlids.
The name has a small backstory. In earlier work on Apoyo's breeding ecology the fish circulated informally as Amphilophus "barlow," a nod to George Barlow, the biologist who spent much of his career on the Midas complex. That honorific was preempted when an Apistogramma was dedicated to Barlow in 2008, so the describers settled on the descriptive epithet supercilius — Latin for "eyebrow" — coined for the strongly developed brow of the neurocranium that gives the fish a frowning countenance.
The holotype is an adult male of 6.5 in standard length (SL), collected on 27 February 2007 along the "Spanish Coast" on the northeastern shore of Lake Apoyo and held at the Zoologische Staatssammlung München (Bavarian State Collection of Zoology) as ZSM 38821; a series of paratypes sits in the same collection. Within Apoyo, Amphilophus supercilius is one of six endemic Midas-complex species — alongside Amphilophus astorquii, Amphilophus chancho, Amphilophus flaveolus, Amphilophus globosus and the elongate Amphilophus zaliosus — that together form a monophyletic, lake-endemic flock. It should not be confused with the Lake Xiloá Midas cichlids (Amphilophus amarillo, Amphilophus xiloaensis and Amphilophus sagittae) that Stauffer & McKaye described from a different Nicaraguan crater lake in 2002; supercilius is an Apoyo fish.
Morphology
This is a moderately large Midas cichlid. The type series tops out at about 6.5 in SL, the figure FishBase carries as the maximum, so a full-grown adult with its tail is on the order of 8 in total. In build it is a fairly deep-bodied, big-headed cichlid in the citrinellus mold, without the extreme elongation of its lakemate the arrow cichlid, Amphilophus zaliosus.
Two features set it apart, in the hand and underwater. The first is the brow that gives the fish its name — a strongly developed portion of the neurocranium bordering the eye socket, which lends it a permanently frowning look. The second, and the single most reliable field mark, is the tail: most of Apoyo's Amphilophus carry a more triangular, pointed caudal fin, but Amphilophus supercilius has a noticeably rounded one, a shape the describers traced to shortened outer (principal ventral) caudal-fin rays and quantified across all six lake species. Together, the brow ridge and the rounded tail let divers tell it from its lakemates.
Breeding fish are dark and dramatic: a gray to dark-green ground color crossed by about seven dark vertical bars — five of them beneath the dorsal fin — plus a dark blotch on the caudal peduncle. The breast and belly go black to dark brown, often with a violet sheen; the pectorals are a yellowish, near-transparent tone, and the rear half of the tail is paler and more translucent. The iris carries a gold rim. Some individuals show a dark spot in the dorsal fin over the third bar, a trait shared with Amphilophus chancho, though whether it tracks sex is not established. As in other Midas cichlids, color here is mood- and condition-dependent rather than fixed, and no consistent external sexual dimorphism beyond the larger size of mature males has been documented.
Habitat
Amphilophus supercilius is endemic to one lake and found nowhere else on Earth: Laguna de Apoyo, a water-filled volcanic caldera on the Pacific slope of Nicaragua, a few kilometers west of Lake Nicaragua. The IUCN assessment puts both the extent of occurrence and the area of occupancy at no more than 14 mi² — effectively the lake itself.
Apoyo is young and self-contained, which is exactly what makes it interesting. The caldera spans roughly 22 mi², the open water about 13 mi², with a maximum depth near 584 ft; the last major eruption that shaped it is dated to roughly 23,000 years ago. The lake sits about 230 ft above sea level and is essentially endorheic — it has no surface outflow, draining only by slow filtration through the porous caldera walls. The water is clear, warm and stays above about 81 °F (81 °F) year-round, and it is faintly mineralized and alkaline.
The fish community is naturally sparse: the Midas cichlid flock, the silverside Atherinella sardina, the livebearer Poecilia, the big predatory Parachromis managuensis, and introduced species. Higher plants are scarce, but from a few meters down the lake grows beds of the macroalga Chara — submerged green meadows that oxygenate the water, shelter juveniles and host the snail Pyrgophorus coronatus that several Apoyo cichlids feed on. Amphilophus supercilius keeps to the lake's sandy bottoms and uses this Chara-fringed benthic zone; unusually, its nests have been recorded across a wide depth band rather than confined to the shallows.
Feeding
Of the six Amphilophus in Lake Apoyo, Amphilophus supercilius has the broadest diet — the describers explicitly called it the most generalist feeder of the flock. Stomach contents have turned up fish remains and fish eggs, molluscs (the abundant lake snail Pyrgophorus coronatus among them), and plant matter in the form of the macroalga Chara. FishBase places it at a trophic level near 3.3, consistent with that omnivorous, opportunistic profile.
That generalism is the ecological point of the fish. Apoyo's cichlid radiation is partly a story of resource partitioning — different members of the flock lean toward snail-crushing, algae-grazing, or open-water feeding — and Amphilophus supercilius occupies the jack-of-all-trades end of that spectrum, taking whatever the sandy, Chara-bedded benthos offers. Its reliance on the Chara meadows and their snails ties its fortunes directly to the health of that habitat, which is why the loss of Chara beds is treated as a conservation flag rather than a footnote.
Mating
Amphilophus supercilius forms monogamous pairs that defend a territory, the standard Central American cichlid pattern. The Cichlid Room Companion summarizes its reproduction as monogamous and cave/substrate-based, and field observation in Apoyo bears that out.
Two behavioral details stand out, and both bear on the species question as much as on natural history. First, the fish mates assortatively: in the wild, the describers' field notes record more than thirty observed pairs, consistently between members of its own species, and that reproductive isolation within a shared lake is part of the evidence that the Apoyo Amphilophus are genuinely distinct species rather than color morphs of one another. Second, its nesting depth is unusually flexible. Most of Apoyo's Midas cichlids breed within a limited depth band, but nests of Amphilophus supercilius have turned up scattered from roughly 7–66 ft down, with no obvious depth preference — a quirk that, together with its generalist diet, paints it as the least specialized member of the flock. As in related Midas cichlids, expect strong territorial aggression from both parents around the nest; that much is a safe inference from close relatives, even though detailed behavioral study of this particular species is sparse.
Breeding
Amphilophus supercilius is a biparental substrate spawner: a pair forms, lays eggs on a cleaned hard surface or in a cave, and both parents guard the eggs and then shepherd the free-swimming fry — the textbook Midas-cichlid mode. Beyond that framework, the specifics for this species are thinly documented in the wild. Clutch size, egg and larval development times, and fry-guarding duration have not been published in detail for Amphilophus supercilius itself, so the honest position is that they are inferred from the closely related Apoyo and Nicaraguan Midas cichlids rather than measured here.
What is distinctive is where the spawning happens. Nests have been recorded across an unusually broad depth range, from about 7–66 ft, with no clear preferred depth — in contrast to lakemates that concentrate their breeding in a narrower band. In Midas cichlids generally the parents tend and fan the eggs through hatching, then move the wriggling larvae between pits in the substrate until the fry are free-swimming and can be led out to forage under close guard. Amphilophus supercilius can reasonably be expected to follow that template, but until targeted fieldwork is done the numbers should be treated as unconfirmed for this species.
In the aquarium
Amphilophus supercilius is essentially unknown in the aquarium hobby. The Cichlid Room Companion records it as never maintained in captivity, and there is no documented captive-breeding program or public-aquarium holding on record. Any fish sold or traded under this name should be treated with deep skepticism: the commercial "Midas" and "red devil" trade is built entirely on Amphilophus citrinellus, Amphilophus labiatus and their hybrids, none of which come from Lake Apoyo. The practical and ethical baseline is that this Critically Endangered single-lake endemic should not be collected from the wild for the hobby.
What follows is a framework for the rare case of a legitimately captive-bred individual — from a research collection or a conservation-breeding project — rather than routine husbandry advice.
Tank: a fully grown fish reaches roughly 8 in total length and is an active, territorial, pair-bonding cichlid. A single pair wants a minimum of 80 US gal, and larger is strongly preferable once breeding aggression intensifies. Standard "Midas-cichlid" setups suit it well, given its use of sandy, Chara-fringed benthos in Apoyo: broken sightlines, ample open sand through the centre, and a few flat stones or a ceramic cave as potential spawning sites.
Water: Apoyo chemistry is hard and alkaline. Barlow, Baylis & Roberts (1976) measured a total hardness of roughly 268 mg/L CaCO₃ and a pH of 8.15 at the surface; the lake runs warm and thermally stable, between about 27 and 86 °F year-round. Match that — pH 7.8–8.5, moderate to hard (GH 10–20 °dH), and a stable 81–84 °F (81–84 °F). Soft or acidic conditions are inappropriate and inconsistent with the fish's natural lake chemistry.
Tankmates: rocky structure for territorial markers and spawning caves works alongside open sand. Planting is largely superfluous — Apoyo's underwater vegetation is the macroalga Chara, not rooted angiosperms — and will be rearranged or uprooted during spawning. This is a large, assertive biparental spawner: once a pair forms and begins breeding, aggression toward any tankmate escalates sharply. Housing it with other cichlids of similar size and temperament is possible in a spacious, heavily broken-up aquarium, but conspecific tolerance outside a bonded pair is low, and mixing it with substantially smaller fish is inadvisable.
Feeding: as the most generalist feeder among Apoyo's Amphilophus, it accepts a broad range of foods — quality cichlid pellets as a base, supplemented with frozen invertebrates (bloodworm, mysis, krill), the occasional small feeder invertebrate, and vegetable matter. Its natural diet spans fish, fish eggs, molluscs and algae, so variety rather than a single staple best reflects that ecology.
Difficulty and availability: the husbandry itself is not unusual for a large Midas-complex cichlid — moderately difficult, suited to an experienced cichlid keeper. The overwhelming obstacle is that the species does not exist in the trade. It is a rare, Critically Endangered endemic of a single 13 mi² crater lake, essentially never collected for the aquarium industry, so a difficulty rating is moot for a fish that cannot legitimately be obtained.
Conservation
The IUCN Red List assesses Amphilophus supercilius as Critically Endangered under criterion B1ab(iii), assessed on 19 July 2019 by Tim Lyons and published in the 2020 update, with a decreasing population trend. The qualifying logic is geographic: the entire species lives in one small, isolated crater lake, with an extent of occurrence and area of occupancy of no more than 14 mi². When a species' whole world is a single lake, anything that degrades that lake threatens the species directly. There is no targeted fishery or aquarium-collection pressure on Amphilophus supercilius specifically — the risk is environmental and lake-wide — and the fish carries no CITES listing.
The central threat the assessors flag is invasive non-native species, above all introduced tilapia (Oreochromis spp.) that escaped fish farms into the Apoyo basin. The concern is well documented in the regional literature: McCrary and colleagues reported tilapia spreading through Nicaraguan waters, Canonico et al. (2005) reviewed the damage introduced tilapias do to native biodiversity, and observers correlated a multi-year disappearance of Apoyo's Chara beds with the herbivorous tilapia — even linking the introductions to an outbreak of eye disease in native cichlids. Because Amphilophus supercilius depends on those Chara meadows and the snails they shelter, the loss of that habitat hits it squarely. Layered on top are the ordinary pressures on a small, accessible lake ringed by a protected reserve: shoreline tourism and development, pollution and garbage, and watershed disturbance.
The wider context raises the stakes. Apoyo is a living laboratory for evolution — Barluenga et al. (2006, Nature 439:719–723) presented it as a leading case of sympatric speciation, the Midas flock having radiated into multiple species within this one young lake. That makes its endemics scientifically irreplaceable as well as ecologically narrow, and the describers framed each new species as another argument for protecting the Laguna de Apoyo Nature Reserve, both as habitat and as a study site. The candid summary: Amphilophus supercilius is not declining because it is hunted or harvested, but because its only home is small, closed and increasingly stressed — and a single-lake endemic has no second refuge to fall back on.