Taxonomy & naming
Described by Paul V. Loiselle in 1997 as Archocentrus myrnae; now placed in Amatitlania, though some authors still use Cryptoheros for the species.
The American ichthyologist and cichlid specialist Paul V. Loiselle described the topaz cichlid in 1997 as Archocentrus myrnae. The type locality is the Río Cocolís, a tributary of the Río Sixaola about 3.5 kilometres southeast of Shiroles in Limón Province, on the Atlantic slope of southeastern Costa Rica. The epithet myrnae is a patronym honouring a person named Myrna. Like the other small convicts, the fish has changed generic homes more than once: it has been carried as Archocentrus myrnae and Cryptoheros myrnae, and now sits in Amatitlania following Schmitter-Soto's 2007 revision of Archocentrus (Zootaxa 1603), which erected Amatitlania, and the Říčan, Piálek, Dragová and Novák revision of Middle American cichlids (Vertebrate Zoology 66, 2016). The generic boundaries among these dwarf convicts remain debated, and some authors still use Cryptoheros. Eschmeyer's Catalog of Fishes and FishBase both list it as valid under Amatitlania myrnae (Loiselle, 1997).
Morphology
A compact convict-shaped cichlid to about 3.1 in SL, pale grey above with a warm topaz-gold flush low on the flanks that deepens in ripe fish.
Amatitlania myrnae is a small, compact cichlid reaching about 3.1 in in standard length (FishBase), with females smaller. The body has the typical oval convict shape, pale grey to bluish above and grading to a warm yellow or topaz-gold flush on the lower flanks and belly — the colour the hobby name records — which intensifies in ripe and displaying fish. Faint dark vertical bars cross the body, usually with one bar more pronounced, and a dark spot or short bar may sit on the caudal peduncle; the markings darken with mood and breeding state. A soft blue or violet iridescence runs through the fins, and in conditioned fish the dorsal and anal fins are edged in pale or reddish tones. Sexual dimorphism follows the usual small-convict pattern: males grow larger, with longer and more pointed dorsal- and anal-fin filaments, while females stay smaller and rounder-bodied and often carry the strongest topaz colour when in breeding condition.
Habitat
A fish of clear, slow Atlantic-slope forest streams in southeastern Costa Rica and adjacent Panama, over sand, gravel and leaf litter at roughly 73–79 °F.
The species lives on the Atlantic (Caribbean) slope of lower Central America, in the Río Sixaola system and neighbouring drainages of southeastern Costa Rica, reaching into adjacent western Panama; FishBase gives the range roughly from the Estrella to the Cuarumo. It favours clear forest rivers and creeks with little current, at modest elevations of about 40–150 metres, over sand, gravel and leaf litter, with submerged wood and rock providing both cover and spawning cavities. FishBase characterises it as a benthopelagic freshwater fish of warm lowland and foothill waters, with a temperature range of roughly 73–79 °F. Its range falls within the Atlantic-slope freshwater fauna of lower Central America — broadly the Río San Juan / Caribbean-Costa-Rica province — a cichlid-rich region of warm, structured lowland rivers.
Feeding
A small benthic omnivore that grazes detritus, ooze, algae and tiny invertebrates from the streambed rather than hunting or sifting sand.
Amatitlania myrnae is a small benthic omnivore that grazes and forages over the bottom. FishBase records its natural diet as plant detritus and ooze — the soft organic film, fine algae and decomposing matter that settle on stones, wood and the substrate — supplemented by the small invertebrates living in it. It is a gleaner and grazer rather than a predator or a true sand-sifter, working the structured margins of its slow forest streams. In the aquarium this makes for an undemanding fish that takes prepared foods readily while still appreciating vegetable matter and small live or frozen invertebrates.
Mating
A monogamous, biparental cave-spawner: a pair claims and defends a cavity, and courtship peaks as the female's topaz colour deepens.
The topaz cichlid is a monogamous, biparental, pair-bonding cave-spawner, and — like the other dwarf convicts — it is comparatively peaceable for a Central American cichlid outside of breeding. A male and female pair off, then together choose and defend a cavity: a crevice among stones, a hollow under wood or an undercut bank in the wild, a cave or pipe in the aquarium. Courtship runs the familiar cichlid course of lateral display, fin-spreading and joint cleaning of the spawning surface, with the female's deepening topaz colour signalling that she is ready. Aggression sharpens around the chosen cave once a pair is in breeding mode, but away from the nest these stay small, relatively mild-mannered fish rather than the tank-clearing bruisers of the larger Central American genera.
Breeding
Adhesive eggs are laid inside a cavity and tended chiefly by the female; broods are modest — around a hundred eggs — and both parents guard the fry.
Amatitlania myrnae is a biparental cave-spawner that breeds readily in suitable conditions. The adhesive eggs are laid on the inner wall or roof of the chosen cavity and tended chiefly by the female, who fans and mouths the clutch while the male holds the surrounding territory. Published clutch sizes for this species are not well documented, but in keeping with its small size the broods are modest — on the order of a hundred or so eggs, smaller than those of the prolific true convict. The eggs hatch within a few days at warm temperatures, the wrigglers are moved to pits, and once free-swimming the fry are led out and guarded as a school by both parents. Care is extended and attentive, and a settled pair will spawn again and again. Where precise fecundity figures are missing, that is stated rather than guessed at: the breeding biology otherwise mirrors that of its close dwarf-convict relatives.
In the aquarium
A manageable, mild small Central American: a pair breeds in a 24–29 US gal tank of caves and leaf litter at 75–81 °F and near-neutral water, given calm, similarly sized tankmates.
The topaz cichlid is a modestly popular aquarium fish among keepers of small Central Americans, valued for its warm colour and its manageable size and temper. A pair can be housed and bred in a tank of around 24–29 US gal, larger in a community.
Tank: echo the home stream — a soft substrate of sand and fine gravel, rounded stones and bogwood arranged into caves and broken sight-lines, leaf litter, and one or more dedicated spawning caves such as an inverted flowerpot or a short length of pipe. Robust plants generally survive, though a spawning pair will tidy a patch around the nest.
Water: track the warm, soft-to-moderate, near-neutral Atlantic-slope streams the fish comes from — temperature around 75–81 °F and pH roughly 6.5–7.5, with moderate hardness, good filtration and regular water changes.
Feeding: easy — a small omnivore takes quality flake and small sinking pellets, with frozen and live invertebrates (bloodworm, daphnia, brine shrimp) and vegetable matter to round out the diet and condition breeders, in line with its natural intake of detritus, algae and small invertebrates.
Tankmates: choose calm, similarly sized fish; avoid both boisterous large cichlids that will bully it and fish small enough to be harassed at spawning time. As with all convicts, give a breeding pair room, since even this mild species defends its fry energetically.
Conservation
Assessed Endangered in 2019 (B1ab(iii,v)) for its narrow, fragmented Atlantic-slope range; hobbyist breeding secures the aquarium strain but not the wild fish.
The IUCN Red List assesses Amatitlania myrnae as Endangered under criteria B1ab(iii,v), assessed on 7 November 2019. The listing reflects a narrow, fragmented Atlantic-slope range in southeastern Costa Rica and adjacent Panama, together with continuing decline in the quality and extent of its habitat: deforestation and sedimentation, agricultural expansion (notably banana and plantation runoff in the Sixaola lowlands), pollution and water-quality degradation, and the spread of introduced species all bear on a fish confined to a small set of clear forest streams. As a narrow-range specialist rather than a wide-ranging generalist, it is more exposed to localised habitat loss than the true convict. The species carries no CITES listing. Because it is bred by hobbyists, the aquarium strain is secure, but the wild assessment is a genuine flag of concern for the fish in its native range.