Taxonomy & naming
Amphilophus viridis was described by Hans Recknagel, Henrik Kusche, Kathryn R. Elmer and Axel Meyer in 2013, in the paper "Two new endemic species in the Midas cichlid species complex from Nicaraguan crater lakes: Amphilophus tolteca and Amphilophus viridis" (aqua, International Journal of Ichthyology 19(4): 207–224, published 25 October 2013). The genus name joins the Greek amphi ("on both sides") and lophos ("crest"); the epithet is simply the Latin adjective viridis, "green," for the green ground colour that sets it apart from its closest look-alike.
The type locality is Lake Xiloá (also spelled Jiloá), Nicaragua, near 12°13′N. The describing authors held the type series at the BMNH (Natural History Museum, London), including specimens registered BMNH 2012.9.2.5 and 2012.9.2.6–7, with further vouchers in the AMCK collection. The fish belongs to the Midas cichlid species complex — the Neotropical radiation built around Amphilophus citrinellus (Günther, 1864) that has become a model system for studying speciation. Within that complex, Amphilophus viridis is one of four Midas species endemic to Lake Xiloá, alongside Amphilophus amarillo, Amphilophus sagittae and Amphilophus xiloaensis (all Stauffer & McKaye, 2002). The original description notes that it resembles Amphilophus amarillo in body shape but differs in colour and ecology and is genetically distinct from all of its lake-mates — a sign that the Xiloá flock is still actively diverging. It has no settled English trade name; the literature calls it descriptively the green Midas cichlid, and in Nicaragua, like the other Midas forms, it is a mojarra.
Morphology
This is a compact, deep-bodied cichlid — short and tall in profile rather than streamlined — reaching about 7.5 in in standard length, so a large adult is a hand-sized fish rather than a monster cichlid. Fin counts run to 16–17 dorsal spines and 11–12 soft rays, with 6–7 anal spines and 8–9 anal soft rays.
Colour is the defining feature. Where the look-alike Amphilophus amarillo carries a yellow ground tone, Amphilophus viridis trends green — the trait the name records. The two are otherwise so alike in body shape and markings that hobbyists generally cannot separate them by eye, and the authors leaned on colour, ecology and genetics rather than gross morphology to tell them apart. A more reliable breeding-season cue helps: the throat of Amphilophus amarillo flushes orange when it spawns, while Amphilophus viridis does not. Like other Midas cichlids, the species can also throw a gold or piebald (xanthic) morph, a polymorphism that recurs across the complex, so any one fish's colour is an unreliable identifier on its own. Sexual dimorphism is weak and not formally quantified here; as in the broader complex, males tend to grow somewhat larger and develop a more pronounced nuchal hump with age, but the sexes cannot be told apart reliably by colour.
Habitat
Amphilophus viridis is a lake fish known only from Lake Xiloá, a small maar crater lake in northwestern Nicaragua. Xiloá sits immediately against the northwest shore of Lake Managua (Lago Xolotlán) at roughly 148 ft above sea level, and its outflow ultimately belongs to the San Juan / Atlantic drainage. It is sometimes filed as a "Lake Managua" cichlid because of that adjacency, but the species has never been recorded from the open waters of Managua — it is restricted to the crater. The original description places it over sandy substrate covered with algae inside the lake.
That restriction is the whole story of the Midas radiation. Ancestral Midas cichlids from the great Nicaraguan lakes colonised nearby crater lakes and then evolved in isolation, each crater a self-contained natural experiment in divergence. Xiloá is geologically young — on the order of a few thousand years — which is why its endemics are still genetically close to one another and to the ancestral stock, and why hybrids still occur. As a bottom-oriented fish, Amphilophus viridis lives along the substrate and lower water column; FishBase classes it as benthopelagic in fresh, tropical water and carries no depth or temperature range for it specifically. Chemistry has not been measured on the species alone, but the lake it is confined to is well characterised: the Barlow, Baylis & Roberts (1976) survey of Nicaraguan crater lakes recorded Xiloá (then "Jiloá") as warm, alkaline and moderately hard — surface-to-95 ft temperatures of about 81–86 °F, the water column well mixed and oxygenated all the way down, a measured pH of 8.00, conductivity of 414 µmhos, and total hardness near 102 ppm as CaCO₃ (roughly 6 °dGH). It is a comparatively eutrophic crater, sitting between the bloom-choked Lake Masaya and the clear, oligotrophic Lake Apoyo. The practical takeaway for anyone keeping Midas-type fish is that this is a hardwater, alkaline Central American crater-lake environment, not a soft Amazonian one.
Feeding
Diet is where Amphilophus viridis genuinely diverges from Amphilophus amarillo, and it is the clearest sign of ecological splitting within the lake. Amphilophus amarillo is a mollusk specialist, its heavy, millstone-shaped (molariform) pharyngeal teeth built to crush snail shells. Amphilophus viridis took the other path: it feeds mainly on algae and plant material, and its pharyngeal jaws carry a much finer, papilliform dentition suited to rasping and rupturing plant and algal cell walls rather than cracking shells. FishBase records the species simply as feeding on plants and algae, at an estimated trophic level around 3.3.
That split — one fish crushing snails, the other grazing plants, in the same small lake — is the kind of resource partitioning that lets several closely related Midas species coexist in a crater only a few square kilometres across. It also feeds the genetic separation: fish that feed differently often spawn differently, and the two lineages stay distinct even while sharing the same water.
Mating
Direct mating observations of Amphilophus viridis are scant — the species was described from preserved material and field collections, not from aquarium spawnings — so most of what can be said is inferred from the Midas complex and from the well-studied Lake Xiloá cichlid community. Midas cichlids are monogamous: a pair forms, bonds, and jointly defends a breeding territory, and they are at their most combative when guarding a brood. The Xiloá assemblage is strongly cavity-dependent for breeding; Kenneth McKaye's classic study of competition for breeding sites among the lake's cichlids (published in 1977 under the lake's older name, "Jiloa") documented how fiercely these fish contest the limited rocky nest holes.
The genetic evidence is itself behavioural evidence. Amphilophus viridis and Amphilophus amarillo remain distinct genetic clusters despite living side by side, which is only possible if the fish mate assortatively — pairing preferentially with their own kind. The fish draw a species line that human eyes struggle to see. Hybrids do occur, as across the young Midas radiation, but assortative pairing keeps the lineages apart. For anyone keeping Xiloá Midas-type fish, the practical upshot is the temperament typical of the complex: territorial, intolerant of its own kind outside of pairing, and prone to letting a single pair dominate even a large tank.
Breeding
No aquarium spawning of verified Amphilophus viridis has been documented, so the account here follows the Midas complex, where the pattern is highly consistent. These are biparental substrate spawners: the pair cleans a hard surface — usually inside a rock cavity or crevice, the limiting resource in Xiloá — and the female lays adhesive eggs that the male fertilises. Both parents guard the eggs and, once they hatch, herd and defend the free-swimming fry for several weeks, shifting them between pits and driving off intruders many times their size. Clutch and fry-development figures for Amphilophus viridis have not been published; for scale, the nominal Midas cichlid Amphilophus citrinellus is a fairly fecund spawner at roughly 300–1000 eggs per clutch (FishBase), and Amphilophus viridis can reasonably be expected to fall in that genus-typical range rather than at any precisely known figure.
Because breeding success in Xiloá turns on access to a defensible cavity, the McKaye competition study is the most relevant field reference: pairs that secure and hold a nest hole reproduce, and the assemblage's intense contest for those holes shapes the whole community. The non-flushing throat of a spawning Amphilophus viridis — versus the orange spawning throat of Amphilophus amarillo — is one of the few breeding-condition traits actually recorded for the species, and it doubles as a field cue for fish in reproductive colour.
In the aquarium
Amphilophus viridis is effectively absent from the mainstream ornamental trade. It is a Vulnerable, single-lake endemic described only in 2013, not exported under its own name, and routinely confused with Amphilophus amarillo even by experienced importers. Anyone keeping it is almost certainly a specialist cichlid breeder who obtained fish through a narrow collector-to-hobbyist chain — the appropriate context for everything below. No aquarium-derived data exist for the species, so tank guidance follows the Midas complex.
Tank: a single specimen needs a footprint of at least 150 × 19.5 in; a genuine pair wants something closer to 180 × 23.5 in, and a 78.5 in tank is better still. Build the hardscape from large, stable rock that creates visual barriers and, above all, enclosed cave or crevice cavities to serve as spawning sites — this fish is obligately cavity-dependent for breeding in the wild. Driftwood is tolerated but will be rearranged; live plants are not a realistic option, since the fish will uproot, dig up and eat them. Protect heaters and filter inlets behind rockwork or use external equipment, because Midas-group cichlids investigate and attack anything exposed.
Water: match the documented chemistry of Lake Xiloá — warm (81–86 °F), neutral to alkaline (pH 7.5–8.5) and moderately hard (up to about 6 °dGH / 102 ppm as CaCO₃). Soft, acidic water is both wrong and unnecessary. Filtration must be robust: the fish is messy, throws a heavy waste load and needs high dissolved oxygen, so oversized canister or sump filtration plus extra surface agitation is practical, with weekly 30–50 % water changes.
Diet: feed the fish's plant- and algae-grazing ecology. A high-quality herbivore or spirulina-enriched cichlid pellet should form the bulk, supplemented with blanched spinach, peas and nori plus occasional invertebrates such as defrosted mysis or krill; carotenoid-rich foods support colour. High-protein mammal-based foods (beefheart, raw red meat) are inappropriate and can cause digestive stress over time.
Tankmates: compatibility is the hardest part of keeping any Midas-complex fish. Amphilophus viridis is a territorial, biparental cave spawner that will dominate and can kill anything entering its perceived territory, especially when breeding. Housing it with other fish at all means a very large tank (upwards of 105–130 US gal minimum) and only large, robust Central American cichlids of comparable size or large armoured catfish; anything small enough to swallow, or unable to escape aggression, will not survive. A breeding pair must be isolated — a tank divider is advisable when first pairing adults, since a male can inflict lethal injuries on a female if introduced abruptly. The safest route is to raise a group of six or more juveniles together, let a natural pair form, and remove the rest as soon as pairing shows.
Difficulty is high — not because the fish is physiologically delicate, but because of its space demands, the aggression to manage and the near-impossibility of sourcing verified specimens. This is a fish for dedicated cichlid specialists, and its Vulnerable status under IUCN D2 (single-lake endemic) puts a responsibility on anyone working with it to keep the lineage pure and, ideally, to document and share breeding results.
Conservation
The IUCN Red List assesses Amphilophus viridis as Vulnerable (VU) under criterion D2, in an assessment by Topiltzin Contreras MacBeath dated 6 February 2020 (published 2020), with the population trend listed as stable. Criterion D2 is the crux: it applies to a species that is not currently declining but whose entire range is so small — here, a single crater lake — that one plausible event could push it toward threatened or extinct very quickly. The species faces no known targeted collection (the trade confusion with Amphilophus amarillo means it is essentially not harvested under its own name), so the risk is environmental and place-based rather than driven by the aquarium hobby. It carries no CITES listing.
That risk is the condition of Lake Xiloá itself, and of the wider Managua basin it abuts. Nicaragua's freshwater fish fauna — catalogued in the recent annotated checklist of the country's continental fishes (Angulo et al., 2023) — is dominated by exactly these narrow-range cichlids, which leaves single-lake endemics structurally exposed. Lake Managua (Xolotlán), against which Xiloá sits, is one of the more polluted large lakes in the Americas, carrying decades of urban and industrial loading before draining south toward Lake Nicaragua. Xiloá is a separate crater, but it is small, comparatively eutrophic and shares the basin's pressures. A documented threat to the country's native cichlids is the spread of introduced tilapia (Oreochromis), widely farmed and now established in natural waters, where they compete with and displace native species; studies single out Xiloá as more affected than the deeper crater Lake Apoyo. The honest framing, then: the fish is not declining today, but it lives in one small, strained lake, and its Vulnerable listing reflects how little margin a single-crater endemic has if pollution, eutrophication or invasive tilapia tip the balance.