Taxonomy & naming
Moenkhausia dasalmas was described in 2011 by Luiz Roberto Malabarba Bertaco, Fernando Carvalho Jerep, and Tiago Pinto Carvalho, with the original account published in Neotropical Ichthyology volume 9. The type locality is a tributary of the rio das Almas in the upper rio Tocantins drainage of Goiás state, Central Brazil. Eschmeyer's Catalog of Fishes (CAS) confirms the valid name as Moenkhausia dasalmas Bertaco, Jerep & Carvalho, 2011, with FishBase entry 66001.
The species belongs to the large and morphologically diverse genus Moenkhausia, a group of characids whose systematics have been in continual revision. Among its congeners, M. dasalmas is distinguished by the combination of iii,9 dorsal-fin rays — a feature that separates it from several similarly proportioned members of the genus — together with a lateral-line scale count of 36–37 and an anal-fin ray count of 17–19 branched rays. Type material includes a paratype deposited at the Universidade Federal do Rio Grande do Sul fish collection (UFRGS 11194) at 1 in SL.
Morphology
Adult Moenkhausia dasalmas are small and slender, reaching a reported maximum of 1.5 in standard length (FishBase). The body form is typical of the genus: fusiform and laterally compressed, with a moderately terminal mouth. Meristic counts from the original description include 36–37 lateral-line scales, iii,9 dorsal-fin rays, and 17–19 branched anal-fin rays — the combination of the dorsal spine-plus-ray count (iii,9) being one of the diagnostic features distinguishing the species from overlapping Moenkhausia in the same drainage.
Detailed colour-pattern information is limited in available records. The species was described from preserved specimens, and vivid in-life colouration has not been extensively reported in the literature. It is likely to show the silvery flanks and translucent fins typical of many small upland Moenkhausia, possibly with a dark caudal-peduncle blotch, though precise markings should be verified against live or freshly preserved material.
Habitat
The species is endemic to the rio das Almas basin in the upper rio Tocantins drainage of Central Brazil, at approximately 2625 ft above sea level. Rio das Almas is a highland tributary flowing through Goiás state, and its fish fauna reflects the elevated, semi-isolated nature of the upper Tocantins headwaters.
FishBase records M. dasalmas as inhabiting streams characterised by semi-lentic to lotic shallow areas no deeper than about 3 ft, with rocky and sandy substrates and well-developed riparian vegetation along the margins. This combination of coarse substrates and overhanging terrestrial vegetation is consistent with the diet (see below) and with the microhabitats used by many small upland characids in the Brazilian cerrado and transition zones. No detailed limnological data for the specific streams are available in the reviewed sources, but highland Tocantins tributaries in Goiás typically run cool to warm, moderately acidic to near-neutral, and relatively low in conductivity.
Feeding
Moenkhausia dasalmas is classified as carnivorous, with a trophic level of 3.2 recorded on FishBase. Diet analysis from wild specimens reveals a strong reliance on allochthonous terrestrial invertebrates: Hymenoptera (ants and wasps) and adult Coleoptera (beetles) dominate the gut contents, indicating that the species feeds heavily on insects that fall from overhanging vegetation or land on the water surface.
Fish scales have also been recorded in the diet, suggesting at least occasional lepidophagy — scale-eating — a feeding mode documented in various Moenkhausia species throughout South America. The combination of surface-oriented insectivory and opportunistic scale-nipping is consistent with the stream microhabitats the species occupies, where riparian insects are seasonally abundant and other small characids are frequent co-inhabitants. In aquarium settings, small live and frozen invertebrate foods, along with high-quality dry foods, would best replicate this carnivorous diet.
Mating
No species-specific mating observations have been published for Moenkhausia dasalmas in the available literature. The broader genus Moenkhausia follows the characid pattern of open egg-scattering with no parental care, and courtship in well-studied congeners typically involves male pursuit and flank-display before a pair-or-group spawning act over submerged vegetation or fine substrate.
Given the species' small size and the stream habitats it occupies — shallow, rocky runs with riparian cover — spawning in the wild likely occurs among fine-leaved aquatic plants or submerged root masses during periods of elevated stream flow associated with seasonal rains in the Central Brazilian cerrado. As with most small upland characids in the Tocantins headwaters, spawning behaviour remains undescribed in detail, and data from the aquarium hobby are also absent owing to the species' scarcity in the trade.
Breeding
No captive breeding records for Moenkhausia dasalmas are available in the reviewed sources. By analogy with other Moenkhausia of comparable size, breeding in captivity would be expected to follow the typical small-characid pattern: egg-scattering over fine-leaved plants or synthetic spawning mops, adhesive or semi-adhesive eggs, no parental care, and a risk of egg predation by the adults if eggs are not removed promptly.
Incubation period and fry requirements are not documented for this species. Breeders working with small upland Moenkhausia generally report short incubation times of 24–48 hours at tropical temperatures, with small fry requiring infusoria or commercial liquid fry food before progressing to newly hatched brine shrimp. Given the species' restricted natural range and very limited presence in the hobby, captive breeding data may not exist outside of specialist research institutions.
In the aquarium
Moenkhausia dasalmas is essentially absent from the ornamental fish trade. Its restricted range in a highland tributary of the upper Tocantins means it has rarely — if ever — appeared in commerce, and no husbandry guidance specific to the species is available. General care principles for small upland Moenkhausia would apply: a well-oxygenated aquarium with gentle to moderate current, subdued lighting, fine-leaved plants or root tangles for cover, and a carnivore-oriented diet of small live or frozen invertebrates alongside quality dry foods.
Water parameters appropriate to its highland Central Brazilian origin would lean toward the cooler end of the tropical range and soft to moderately hard, near-neutral chemistry — though exact preferences remain undocumented. Given its documented reliance on terrestrial insects in the wild, surface-feeding behaviour should be anticipated. Any aquarist fortunate enough to obtain this species should prioritise careful acclimation and document behaviour and breeding outcomes, as such records would represent a genuine contribution to knowledge of this poorly known taxon.
Conservation
The IUCN Red List assessed Moenkhausia dasalmas as Least Concern in November 2018, based on a population judged to be stable within its known range in the rio das Almas basin. The assessment noted no major threats sufficient to warrant a more precautionary listing at that time.
Despite the Least Concern status, the species' narrow endemism — confined to a single highland tributary system — means that large-scale land-use change in Goiás, catchment degradation, or water extraction from the upper Tocantins headwaters could pose future risks. The cerrado biome, in which the rio das Almas basin sits, has experienced severe habitat conversion across much of its extent over the past half-century. Future reassessments should consider whether ongoing cerrado loss and agricultural intensification in Goiás are affecting the quality and connectivity of the streams this species depends on.