Taxonomy & naming
The blackthroat cichlid was described by Albert Günther in 1864, originally in the genus Heros. Over the following century and a half it was shuffled through the usual sequence of Central American cichlid genera — Cichlasoma, then Amphilophus — before Oldřich Říčan's work on the Middle American heroines (culminating in the 2016 revision) restricted the genus Astatheros (erected by Pellegrin in 1904, with macracanthus as its type) to this single species, while transferring the related substrate-sifters once placed in Astatheros (alfari, altifrons, bussingi, diquis, longimanus, rhytisma, robertsoni, rostratus) to the new genus Cribroheros. Astatheros macracanthus is therefore now monotypic — the only valid species in its genus. The epithet macracanthus ('long-spined') refers to the elongate fin spines. The genus belongs to the heroine cichlids (tribe Heroini); the name Astatheros combines a Greek root with the heroine -heros.
Morphology
Astatheros macracanthus is a robust, moderately deep-bodied cichlid reaching about 10 in SL. The body is silvery-grey to olive or tan, often with a greenish or golden sheen, marked with a series of dark vertical bars or blotches along the flank that strengthen or fade with mood, and frequently a dark midlateral and caudal-base spot. The unpaired fins may carry fine spangling and reddish or orange margins. The species' English name comes from a conspicuous dark patch that develops on the throat and lower head of fish in breeding condition. The mouth is sub-terminal, suited to its substrate-sifting habit. Sexual dimorphism follows the heroine pattern: mature males grow larger and develop more produced, pointed dorsal and anal fin tips, while ripe females are deeper-bodied through the belly and may show the dark throat patch and intensified barring more strongly when breeding.
Habitat
Distinctively for a Central American cichlid, Astatheros macracanthus is a Pacific-slope species: it ranges along the Pacific drainages from the Tehuantepec region of southern Mexico (Chiapas) through Guatemala to El Salvador. It inhabits warm lowland rivers, their slower reaches and floodplain lagoons, and coastal lowland waters, typically over soft substrates of sand and mud where it can sift for food. The water across this range is warm and generally hard and alkaline; FishBase cites roughly 79–86 °F and pH from about 7.5 upward. The species occupies the warm, productive lowland and coastal-plain waters of the Pacific versant, a setting drier and more seasonal than the Caribbean slope and with a distinct, less diverse cichlid fauna in which the blackthroat is a characteristic member.
Feeding
Astatheros macracanthus is a benthic omnivore and substrate-sifter, FishBase placing it at a trophic level near 3.3. It feeds by taking mouthfuls of soft sediment and sorting out the edible fraction — small invertebrates (insect larvae, crustaceans, worms), with organic detritus and some plant material — expelling the sorted substrate through the mouth and gills in the winnowing manner of the sand-sifting heroines. The sub-terminal mouth and the genus's feeding mechanics suit this bottom-oriented diet. In the lowland river and lagoon communities of the Pacific slope it functions as a generalist forager of the soft-sediment zone, a role analogous to that of its Caribbean-slope relatives in Cribroheros.
Mating
As a heroine cichlid, Astatheros macracanthus is a monogamous, biparental species that pairs and defends a joint breeding territory. Pair formation follows the standard cichlid sequence — lateral display, fin-flaring, jaw contact and cooperative cleaning of a spawning surface — with the pair intensifying in colour and territoriality as spawning nears; the dark throat patch that names the species is most evident at this time. The species is moderately aggressive, with territoriality rising sharply at breeding. Pairs select and clean a hard surface in advance of spawning.
Breeding
Astatheros macracanthus is a biparental open substrate spawner. The female lays a clutch of adhesive eggs on a cleaned hard surface, and both parents share extended care: the female tends and fans the eggs while the male guards the territory, the roles converging as the brood develops; once free-swimming the fry are guarded as a school by both parents, who lead them over the soft bottom where they begin to forage. Clutch sizes are in the several-hundred range typical of a medium-large heroine. Wild breeding behaviour is not exhaustively documented, but it follows the well-established biparental-substrate-spawner pattern of the group, and the species has been bred in captivity by specialists following that approach.
In the aquarium
The blackthroat cichlid is an uncommon aquarium fish, kept mainly by Central American cichlid specialists rather than in the general trade, but it is a manageable substrate-sifter for those who can source it. A single adult or a pair needs a tank of at least about 80–105 US gal, with ample floor space valued by a bottom-oriented fish. Water should be warm (79–86 °F) and hard and alkaline (pH about 7.5–8.2), reflecting its Pacific-lowland origins; the species is not a soft-water fish. Strong, well-maintained filtration and generous water changes suit a robust fish on a sediment diet.
The single most important furnishing is a deep bed of fine sand: as a substrate-sifter the fish needs sand it can take into its mouth and process, and a sand bottom lets it express natural feeding behaviour while sparing its gills the abrasion that gravel can cause. Furnish with rock and driftwood structure forming broken sight-lines and a flat stone as a spawning site; hardy, anchored plants survive a moderate digger. As a moderately aggressive, territorial cichlid it is best kept with other robust Central American fishes of similar size and temperament, with breeding pairs given space or their tankmates managed at spawning time; small or timid fish are unsuitable. Feeding is straightforward — a quality sinking cichlid pellet staple plus frozen and live invertebrate foods (bloodworm, brine shrimp, prawn) and some vegetable matter; the sand bottom encourages natural sifting between feeds. The chief husbandry notes are to provide sand rather than gravel and to respect the hard, alkaline water it comes from.
Conservation
The IUCN Red List assesses Astatheros macracanthus as Least Concern (assessed 2018), reflecting a reasonably wide distribution along the Pacific slope from southern Mexico to El Salvador and populations not considered to be in overall decline. It is taken locally for food and occasionally for the ornamental trade, but neither is regarded as a population-level threat. The Pacific-slope lowland waters it inhabits are nonetheless exposed to the region's familiar pressures — agricultural runoff and pesticide pollution, water extraction for irrigation in a seasonally dry landscape, deforestation, and introduced species — which are watch-points for the future rather than documented threats to this fairly adaptable species at present. It carries no CITES listing.