Taxonomy & naming
Amphilophus astorquii was formally described in 2008 by Jay R. Stauffer Jr., Jeffrey K. McCrary, and Kristin E. Black, in a paper naming three new cichlids from Lake Apoyo (Proceedings of the Biological Society of Washington 121:117–129). Eschmeyer's Catalog of Fishes lists the holotype as PSU 4518.1 and the type locality as Casa Rosal on Lake Apoyo (11°55.74'N, 86°3.18'W), with paratypes at the American Museum of Natural History (AMNH 240557) and Penn State. The Catalog and FishBase both treat the name as valid under that authorship; some popular sources wrongly credit 'McKaye & Konings,' but the describing trio is Stauffer, McCrary & Black.
The species sits in the Amphilophus citrinellus species complex, the New World answer to the African rift-lake radiations, and belongs to an endemic flock that arose inside Apoyo itself. It is the lake's compact-bodied, thin-lipped 'normal' form — distinct from the slender, open-water arrow cichlid (Amphilophus zaliosus) and from congeners such as Amphilophus chancho, Amphilophus flaveolus, Amphilophus globosus, and Amphilophus supercilius — and reads as the shallow-benthic, hard-prey member, the Apoyo analogue of Amphilophus amarillo in nearby Lake Xiloá. Nicaraguans simply call the lake's cichlids mojarras; FishBase's 'black midas cichlid' is a manufactured descriptor rather than an established trade name, so it is noted here but not elevated to a common name.
Morphology
This is a genuinely small cichlid by Amphilophus standards. The largest specimen in the original description measured 6 in standard length — the figure FishBase carries as the maximum — while the described series averaged only about 4.5 in. It is short and deep-bodied with thin lips, lacking the exaggerated fleshy lips of the red-devil line; fin counts run to 16–18 dorsal spines and 10–12 soft rays, 6–7 anal spines and 8 anal soft rays, with the snout-to-dorsal-origin distance 41.1–47.9% of standard length.
Out of breeding it wears standard Midas livery: a greenish to greyish ground broken by a row of dark dorsolateral blotches. Spawning transforms it — the caudal peduncle and head turn jet black and the side-blotches can spread into bars that merge until much of the fish looks nearly black, the trait behind the 'black midas' descriptor. The gold (xanthic) morph common in the great Nicaraguan lakes is absent from Apoyo, so no bright orange individuals occur here. Telling it from its lakemates is subtle: it tends greenish where the arrow cichlid runs silver, and the two become reliably distinguishable only at about 3 in, while the other compact Apoyo species average a little larger. Sexual dimorphism is the usual cichlid pattern — males grow larger than females — without a strong year-round colour difference between the sexes.
Habitat
Amphilophus astorquii is a lacustrine endemic in the strictest sense: its whole world is Laguna de Apoyo, a water-filled volcanic caldera straddling the departments of Masaya and Granada. The lake is young in geological terms — on the order of 23,000 years old — roughly circular and about 3 mi across, with a maximum depth usually given near 574–656 ft and a surface area around 13 mi² (8 sq mi). Being endorheic, it has no river outlet, so its waters are mildly mineralized, warm, and clearer than the surrounding turbid great lakes; it is also oligotrophic and thermally stable year-round, with an alkaline surface pH around 8.5–9 and comparatively high conductivity.
The fish keeps to the near-shore zone, where rocky reefs give way to sand and to beds of stonewort (Chara) that carpet the bottom from a few metres down to roughly 59 ft. It favours rocky structure but readily uses open, featureless bottom too, and nesting has been recorded around 41 ft, slightly deeper than the arrow cichlid's preferred band — the shallow-benthic specialist of a flock that partitions the lake by depth and body form.
Feeding
Among Lake Apoyo's Amphilophus, Amphilophus astorquii is the shallow, bottom-oriented species that works hard-shelled prey — not the biofilm grazer its small size might suggest. Comparative studies of the Nicaraguan crater-lake radiations cast it as the littoral hard-diet form, the Apoyo counterpart of Amphilophus amarillo in Lake Xiloá: a benthic feeder taking snails and other molluscs alongside aufwuchs (the film of algae and small invertebrates on rock), insect larvae, and worms picked from the substrate. Its lower pharyngeal jaw leans toward the robust, crushing (durophagous) shape, though the molariform–papilliform split is less sharp inside Apoyo than in Xiloá, and FishBase places its trophic level near 3.3. Species-specific gut-content data are thin, so the safe statement is functional: it is the shallow-benthic, snail-and-aufwuchs feeder of the lake.
Its wider role is as a keystone of a simple, isolated community. Before African tilapia (Oreochromis) were introduced, Apoyo held essentially only this endemic cichlid flock plus the predatory guapote (Parachromis managuensis), and nest counts at three sites (McCrary & López 2008) found Amphilophus astorquii dominating the breeding sites — far more than any other species — which is why it is reckoned the flock's single most abundant fish.
Mating
Like the rest of the Midas complex, Amphilophus astorquii forms monogamous pairs that defend a territory together, and in breeding condition both fish turn strongly territorial — in the wild, that means competing for the best nesting holes in the rocky littoral. Males grow larger than females, and pair formation comes before the cleaning and claiming of a spawning surface, usually a crevice or hollow among rocks, though pairs will also settle over plain substrate away from structure.
In Apoyo the species eases that competition by partitioning breeding in time and depth: it nests most heavily in November and December, while the arrow cichlid peaks in October and February, so the two crowd the reef sites in different months and, where they overlap, at slightly different depths. The aggression is not only a wild trait — a laboratory study of aquarium aggression and welfare (Oldfield 2011) used this species and found that even reproductively immature juveniles showed measurable territorial aggression, which added physical structure in the tank helped diffuse.
Breeding
Amphilophus astorquii is a biparental substrate spawner, not a mouthbrooder. A pair cleans a surface — usually inside a hole or crevice among rocks, sometimes over open bottom — and the female lays adhesive eggs that both parents then guard, together with the fry once they hatch. Care runs long: the adults tend the free-swimming young for roughly six weeks, often shepherding the school out over open substrate where the fry can pick microscopic food from the water column and from periphyton. Nest counts in Apoyo found Amphilophus astorquii dominating the breeding sites, with the arrow cichlid reaching only about five percent of nests at the surveyed reefs.
Clutch figures specific to wild fish are not well documented; like its Midas-complex relatives it lays a substrate clutch on the order of a few hundred eggs, and FishBase's life-history model assumes a fecundity under 1,000. What is well established is the mode — the dark-cavity nest preference and the extended biparental guard — while exact egg counts and fry-growth milestones for this particular fish remain thinly reported in the primary literature.
In the aquarium
Amphilophus astorquii is essentially not a trade fish; it is kept almost entirely in research and specialist settings. The best-documented captive work is Oldfield (2011) on how tank size and structure affect aggression, with Mandrekar & Oldfield (2008) on juvenile territoriality. Treat it as what it is: a small, intense, biparental substrate spawner from a chemically distinctive crater lake, not a standard Central American cichlid.
Tank: footprint matters more than volume. Oldfield found that even non-breeding juveniles turned severely aggressive in a standard 75-litre (20-gallon) high — dominant fish monopolising the space while subordinates cowered in the corners — whereas a five-foot, roughly 380-litre (100-gallon) tank packed with rock, caves, and plants cut that aggression sharply. For a pair, plan on at least a 47 in floor length, since breeding adults are far more aggressive than juveniles and need real territory plus visual barriers a subordinate can hide behind.
Water: mirror the crater lake — warm, hard, and alkaline, at 79–86 °F (79–86 °F) and pH about 8.5–9.0 with high mineral content. Soft or acidic water is wrong for the fish and will suppress its immune system and likely block breeding; because Apoyo is oligotrophic, keep the bioload low and the filtration efficient.
Tankmates: choose with caution or skip them. A breeding pair attacks anything it reads as a threat to the nest, and even out of condition two similar-sized fish may fight, so a pair is safest kept alone — this is not a community fish.
Common mistakes: under-sizing the tank; giving one shelter instead of several (Mandrekar & Oldfield 2008 found juveniles fought over a single ceramic pot, so distribute several refuges); soft water; and treating an intermediate-difficulty cichlid as a beginner's fish. Fine sand or gravel suits its benthic foraging, and a sinking-pellet staple plus frozen or live invertebrates — bloodworm, mysis, small snails — matches its natural hard-prey diet. Captive lines outside research institutions are almost unknown, so insist on traceable provenance and treat any breeding as a conservation responsibility.
Conservation
The IUCN Red List assesses Amphilophus astorquii as Critically Endangered under criterion B1ab(iii) (assessor Tim Lyons; assessed 15 July 2019), with a decreasing population trend. The listing is not driven by scarcity in the lake — it is one of the commonest fishes there — but by geography: confined to a single small water body, its extent of occurrence is tiny, so any decline in habitat quality counts against its entire global range at once. It is not CITES-listed and is rated of low fishing vulnerability, with no fishery aimed specifically at it; the risk is structural, the price of living in only one place.
Laguna de Apoyo lies inside a designated nature reserve yet faces shoreline residential and commercial development, deforestation of the crater walls, dropping water levels, and the resulting shifts in water chemistry — all bearing on the near-shore zone where this fish breeds and feeds. The introduction of African tilapia (Oreochromis) is a documented concern, competing for the algal beds the natives depend on, and a rapid census of the lake's Amphilophus put the whole flock's adult population below 100,000 fish. The honest summary is not that Amphilophus astorquii is collapsing today, but that an abundant fish with a one-lake range has almost no margin for error: protecting the species is, functionally, the same problem as protecting Laguna de Apoyo itself.