Taxonomy & naming
Acestrocephalus maculosus was described by the Brazilian ichthyologist Naércio Aquino Menezes in 2006 in a paper published in Neotropical Ichthyology (vol. 4, no. 4), alongside four other new species of Acestrocephalus: A. stigmatus, A. nigrifasciatus, A. acutus, and A. pallidus. The holotype (MZUSP 53974, 3 in SL) was collected in May 1996 by Miguel T. Rodrigues and colleagues from córrego Água Parada, a tributary of the rio do Peixe at Serra da Mesa, municipality of Minaçu, Goiás, Brazil. The Catalog of Fishes records the valid name as Acestrocephalus maculosus Menezes, 2006.
Acestrocephalus belongs to the family Characidae and to the tribe Acestrorhynchinae in some classifications, a group of slender, predatory characins with prominent teeth. The genus was established by Eigenmann and has been subject to periodic revision; Menezes's 2006 paper provided the most thorough treatment of the group at the time, adding the five new species and redescribing A. sardina and A. boehlkei. Within Acestrocephalus, A. maculosus is distinguished from most congeners by the presence of a dark humeral blotch — a character shared only with A. boehlkei and A. stigmatus among the species treated in the 2006 revision — combined with an anal-fin ray count of 25–27 and 7–8 gill-rakers.
Morphology
Acestrocephalus maculosus is a small, elongate fish. The holotype measures 3 in SL (approximately 3 in), and FishBase records the maximum size as 3 in SL. In the original description, examined specimens ranged from 1.5–3 in SL. The body is slender and laterally compressed, typical of predatory Acestrorhynchinae, with a pointed snout and enlarged, conical teeth suited to capturing smaller fish and invertebrates.
The most diagnostic external character is the dark humeral blotch situated just behind the opercle. The specific epithet maculosus is derived from the Latin for 'spotted', referring to the pattern of dark spots and stripes on the body. Meristic counts recorded in the original description include dorsal-fin rays ii,9, anal-fin rays iv,27, and a complete lateral line with approximately 73 scales. Gill-raker counts of 7–8 on the first arch further help separate this species from congeners with differing counts.
Habitat
The type locality is a small, clear-water stream — córrego Água Parada, a tributary of the rio do Peixe in the Serra da Mesa region of Goiás — at an elevation above the broad floodplain of the lower Tocantins. FishBase places the species in the upper Tocantins basin, which drains a portion of the Brazilian cerrado highlands before descending to the reservoir of Serra da Mesa, one of Brazil's largest hydroelectric impoundments completed in 1998.
Water conditions reported by FishBase for this taxon indicate warm water around 77 °F and a mildly acidic pH of approximately 6.5, consistent with the clear, soft to moderately soft headwaters typical of cerrado streams. Beyond the type locality and broad drainage assignment, detailed habitat data for this species in the published literature are sparse.
Feeding
Acestrocephalus species are regarded as insectivorous to piscivorous predators, and FishBase characterises A. maculosus as insectivorous. The slender body shape, large mouth, and prominent dentition of Acestrocephalus are consistent with an active pursuit predator that takes invertebrates and, at larger sizes, small fish.
Detailed dietary studies specific to A. maculosus have not been published. By analogy with the feeding ecology of related Acestrorhynchinae and other predatory characids of the cerrado stream fauna, the species likely consumes aquatic and terrestrial insects, small crustaceans, and opportunistically takes smaller fish when available.
Mating
No published observations of mating behaviour exist for Acestrocephalus maculosus. Members of the family Characidae broadly are egg-scattering open spawners that deposit adhesive or semi-adhesive eggs among fine-leaved vegetation or over substrate, with no parental care following spawning. Whether A. maculosus follows this general characid pattern, or displays any spawning-site fidelity or aggregation behaviour, is undocumented.
For predatory Acestrorhynchinae more broadly, reproductive biology is poorly studied. Seasonal breeding tied to the cerrado wet season (roughly October–March) is plausible given the strongly seasonal hydrology of Tocantins headwater streams, but this is inference from the regional context rather than published data specific to this species.
Breeding
Acestrocephalus maculosus has not been bred in captivity under documented conditions, and there is no published breeding account for this species. As a predatory characid it would presumably follow the general egg-scattering mode: adults scatter small adhesive eggs among fine-leaved plants or over gravel substrate, with eggs hatching after a few days at tropical temperatures and fry requiring small live foods.
The predatory temperament of Acestrocephalus makes captive breeding logistically challenging — adults will readily eat fry and smaller tankmates, and isolating a breeding pair or removing eggs promptly after spawning would be essential. No aquarium literature on captive reproduction of this species was located.
In the aquarium
Acestrocephalus maculosus is essentially unknown in the aquarium hobby. It does not appear in mainstream hobby literature or trade catalogues, and is rarely if ever available commercially. The species is a specialist predator with a small adult size (under 3 in SL) that might in principle make it manageable in a dedicated species or biotope aquarium, but the absence of established husbandry knowledge means any keeper would be working without a reliable precedent.
For those interested in the species as part of a cerrado biotope project, water conditions approximating the type locality — temperatures around 77 °F, mildly acidic to neutral pH, good oxygenation, and clear water with moderate flow — would be a reasonable starting point. Tank companions would need to be chosen carefully given the predatory nature of the species; fish significantly smaller than A. maculosus should be avoided. Data on captive care are sparse enough that no confident care rating can be assigned.
Conservation
Acestrocephalus maculosus is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment dated 7 November 2018. The DD designation reflects insufficient data to determine the species' range, population size, or trajectory — not a conclusion that it is unthreatened. The type locality lies within the watershed of Serra da Mesa reservoir, a large hydroelectric impoundment completed in the late 1990s that inundated extensive cerrado river habitat in Goiás. The extent to which upland tributaries like córrego Água Parada were affected, and whether populations of A. maculosus persist above the reservoir's influence, is not documented in the available literature.
The broader context of endemic cerrado stream fishes is one of significant threat from agriculture-driven deforestation, sedimentation, water extraction, and river impoundment. A species known from a single drainage and restricted to headwater streams is inherently vulnerable to such pressures. A future reassessment with survey data from the type locality and surrounding streams would clarify whether the DD status masks a more precarious situation.