Taxonomy & naming
Albert Günther described this fish in 1867 as Heros trimaculatus, from the Pacific slope of southern Mexico; the commonly cited type locality is San Gerónimo, Oaxaca. It shares its epithet with an unrelated African fish, the Lake Malawi cichlid Copadichromis trimaculatus, but the two have nothing else in common. Like nearly all Middle American cichlids it spent decades in the catch-all genus Cichlasoma — and the hobby still very widely calls it 'Cichlasoma trimaculatum' — before being moved to Amphilophus. The Catalog of Fishes and FishBase now list it as valid under Amphilophus trimaculatus (Günther 1867). It sits among the heroine cichlids of subfamily Cichlinae, on the Pacific-slope wing of the genus. Some recent classifications have floated moving the trimac and its allies into other resurrected Middle American genera, but the Amphilophus combination remains the standard valid name in the Catalog of Fishes. The epithet trimaculatus is Latin for 'three-spotted,' after the dark blotches along the side; the number of conspicuous spots actually varies, but the name fixed on three.
Morphology
Amphilophus trimaculatus is a large, deep-bodied, powerfully built cichlid — one of the bigger members of its genus — reaching about 14.5 in standard length in males (FishBase), with females somewhat smaller. The body is robust and laterally compressed, the head large and strong-jawed, and dominant breeding males develop the pronounced nuchal hump typical of the big Amphilophus. Colour is what won the species its following. Over a tan to grey or olive ground sit the dark mid-lateral blotches that name the fish and a spot at the caudal-fin base; most striking is a flush of brilliant red to orange across the throat, chest and lower flanks, picked out with iridescent blue-green spangling on the body and fins. That red intensifies dramatically in breeding and dominant individuals, and both its depth and the size of the hump track a fish's condition and rank — a well-coloured male is a spectacular animal. Dimorphism is strong: males grow much larger, build the hump and longer fin extensions, and carry the most intense red, while ripe females stay smaller and rounder and often show a darker, higher-contrast breeding dress.
Habitat
The three-spot cichlid is a Pacific-slope fish of Middle America, ranging from western and southern Mexico south through the Pacific drainages of Guatemala to the Río Lempa in El Salvador; FishBase gives the range as the Pacific-slope rivers from Mexico to El Salvador, with the Mexican end reaching the Laguna de Coyuca area. It is a lowland species of warm, often slow-moving or still water — rivers, lagoons, coastal lakes and floodplain pools — and is recorded tolerating brackish conditions in coastal lagoons, an unusual trait that feeds both its hardiness and its wide spread. FishBase gives a temperature range of roughly 70–86 °F across the warm Pacific lowlands it occupies. This is a tough, adaptable fish that does well in the variable, seasonally fluctuating waters of the coastal plain, from clearer rivers to turbid lagoons — the same versatility that underlies its broad natural range and its reputation as an undemanding aquarium fish.
Feeding
Amphilophus trimaculatus is a large predatory omnivore. FishBase records a diet of small fishes, macro-invertebrates and aquatic and terrestrial insects, and places it fairly high on the food web at trophic level about 3.4 — well above the small sand-sifters and detritivores of its range. Its big mouth and strong jaws let it take sizeable prey, and in the wild it works as a robust predator-omnivore of the lowland waters, hunting small fishes and large invertebrates while also snapping up insects that fall onto the surface. That opportunism carries over to the aquarium, where the trimac is an eager, even greedy feeder — the same flexible appetite that lets it thrive across clear rivers and turbid lagoons alike.
Mating
As a large Amphilophus, the three-spot cichlid is a biparental, pair-bonding substrate spawner with intense, conspicuous courtship. A male and female form a strong pair bond and, together, establish and defend a sizeable territory around a chosen spawning site. The courtship is the full-genus display — lateral posturing, fin-spreading, head-down quivering, vigorous mutual jaw-locking trials of strength, and cooperative cleaning of the spawning surface — all staged in heightened breeding colour, the male's red throat and chest at their most vivid and his hump most swollen. In the confines of a tank, pairing is famously fraught: a male and female must be introduced with care, because the aggression that fuels their territorial defence can just as easily be turned on an unready partner. Once bonded, though, the pair becomes a formidable and devoted breeding unit.
Breeding
Amphilophus trimaculatus is an open or semi-open biparental substrate spawner and a prolific, attentive parent. The adhesive eggs are laid on a cleaned hard surface — a flat stone, a slab, or a scraped patch of substrate — and both parents share an intense care regime: the female fans and tends the clutch while the male defends a wide perimeter. Once the eggs hatch, the wrigglers are shifted to pits, and the free-swimming fry are herded and guarded as a large school by both adults. Spawns run large for a big cichlid, commonly several hundred and up to a thousand or more eggs in well-grown pairs, and the brood defence is fierce enough that a breeding pair will drive off fish far larger than themselves. In the wild, spawning tracks the favourable season of the Pacific lowlands. In the aquarium the species breeds readily once a compatible pair settles — a big part of its popularity, though the aggression that comes with breeding is the catch.
In the aquarium
The trimac is one of the classic large Central American cichlids of the hobby, kept for its size, its brilliant red colour and its bold, intelligent personality, and it has a long history in the trade under the name 'Cichlasoma trimaculatum.' It is hardy and easy to feed, but it is also a big, seriously aggressive fish — one for keepers ready to provide properly for it.
Tank: at an adult size around 14 in, a single fish needs a large aquarium — on the order of 105 US gal or more, with a long footprint — and a breeding pair or any tankmates need considerably more. Give it robust, secured decor (large rocks and wood) that a powerful digger cannot dismantle, open swimming space, and flat surfaces that can double as spawning sites.
Water: warm and on the hard, neutral-to-alkaline side its range suggests — around 75–86 °F and pH roughly 7.0–8.0 — with strong filtration and generous water changes for a large, messy, high-output fish. Its brackish tolerance makes it forgiving of harder water.
Feeding: a varied diet of quality pellets, frozen and live foods and meaty items suits its predatory-omnivore nature; hold back a little, because it will happily overeat.
Tankmates: temperament is the defining issue. The trimac is territorial and powerful, and breeding pairs are exceptionally aggressive, so any tankmates must be large and robust and the tank big enough to defuse conflict — many keepers simply run it singly or as an established pair.
Common mistakes: under-sizing the tank, under-filtering, and underestimating just how much aggression a breeding pair generates.
Conservation
The IUCN Red List assesses Amphilophus trimaculatus as Least Concern (assessed 27 November 2018). It ranges widely across the Pacific slope of Middle America from Mexico to El Salvador, and as a hardy generalist — at home in warm, turbid and even brackish coastal water — it is far more resilient than the narrow-range crater-lake endemics elsewhere in the genus. It is common across much of its range and of only minor local fishery and ornamental interest. The assessment lists the usual regional pressures on Pacific-slope lowland waters — pollution from agriculture and wastewater, habitat alteration, water management and the spread of non-native species — but none rises to a population-level threat for so widespread and adaptable a fish, and its status is considered secure. It carries no CITES listing. If anything, as a robust, established aquarium and pond fish, Amphilophus trimaculatus is among the Central American cichlids that have themselves been introduced beyond their native range — more a potential invasive in some settings than a species of conservation concern.