Taxonomy & naming
Gasteropelecus maculatus was described by the Austrian-Brazilian ichthyologist Franz Steindachner in 1879. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer and Fong) records the valid name as Gasteropelecus maculatus Steindachner, 1879, with a type specimen later deposited at the Field Museum (FMNH-56055). The species belongs to the family Gasteropelecidae — the freshwater hatchetfishes — a wholly Neotropical group of deep-keeled, surface-dwelling characiforms with no valid relatives outside the Americas. Within the family, Gasteropelecus is the largest genus in terms of body size; the three species are separated chiefly by maximum size and spotting pattern.
Taxonomy of the species was confirmed valid by Eschmeyer and Fricke (2016), which is the standard the DePaul University Western Ecuador Fishes database follows. The spotted hatchetfish is the only member of the genus with a range spanning both Pacific-slope and Atlantic-slope drainages in north-western South America, giving it the broadest known distribution in the genus. Its placement within Gasteropelecidae has not been seriously contested in modern literature.
Morphology
Like all gasteropelecids, G. maculatus is immediately recognisable by the extreme ventral keel formed by the enlarged sternal bones and the massive pectoral-girdle musculature packed inside. Viewed from the side, the fish presents almost a right-angle between the vertical chest wall and the near-horizontal dorsal profile. Maximum standard length is recorded at about 2.5 in SL in specimens from Ecuadorian material, with common sizes around 2 in SL, though FishBase records some individuals reaching 3 in SL; total length may approach 3.5–4.5 in in the largest fish.
The body is silver, often with a faint iridescent or brassy sheen along the lateral line region, and is overlaid with irregular dark spots or blotches that give the species its common name. These markings are more pronounced in some populations than others and may fade somewhat in stressed or recently caught fish. The enlarged pectoral fins are oriented nearly horizontally and are the engine of the species' remarkable surface locomotion and short-distance "flight". The dorsal fin is short and set far back; the adipose fin is present.
Habitat
The spotted hatchetfish occurs in freshwater lowland systems from eastern Panama south through the Colombian Pacific-slope rivers (Atrato, San Juan, Baudo, Calima) and into Ecuador's Esmeraldas Province and the Santiago-Cayapas drainage. Outside the Pacific slope, it has been recorded in Atlantic-drainage rivers including the Rio Meta in the Orinoco system, and some sources list the Amazon basin more broadly. It inhabits clear to semi-clear waters with sandy substrates and decomposing leaf and plant material.
As a surface specialist, G. maculatus stays close to the film in slow-moving or still sections of rivers, lagoon margins, and flooded forest edges. Flow regime is mild — the species prefers areas with little current, consistent with the Fishipedia report of slow or near-stagnant conditions. Water parameters recorded from the field and aquarium data suggest temperatures of 72–82 °F, pH 6.0–7.0, and general hardness up to about 15 dH, placing it in soft to moderately soft, slightly acidic lowland waters typical of the region's blackwater and clearwater rivers.
Feeding
Gasteropelecus maculatus is a surface-feeding carnivore specialising on invertebrates at or above the water surface. Field data from Ecuadorian specimens document a diet of hymenopteran, dipteran, and coleopteran insects together with plant material and occasional fish remains — the profile of a fish that picks from the surface film and takes airborne insects on the wing during its leaping bursts.
The enlarged pectoral musculature serves both escape and prey capture: the fish can use a rapid surface sprint to intercept prey items just above the film. In the aquarium, it accepts small live and frozen invertebrates such as fruit flies (Drosophila), mosquito larvae, brine shrimp, and small bloodworm. High-quality floating flake or micro-pellets are also accepted once the fish has settled. All food should be offered at the surface or allowed to drift there; bottom-presented food is typically ignored. Feeding frequency and quality strongly influence the fish's condition and willingness to spawn.
Mating
Gasteropelecus maculatus is an egg-scattering open spawner with no parental care, following the general pattern of the family. Females are reportedly larger than males — the typical sexual dimorphism in the genus, with ripe females visibly broader across the abdomen when viewed from above. Males are otherwise similar in appearance, and the species lacks the pronounced secondary sexual characters of many cichlids or bettas.
Courting behaviour in the wild is poorly documented, but by analogy with related hatchetfishes, males likely pursue females in the surface zone, and spawning is triggered by warm, soft, acidic conditions. Eggs are scattered among fine-leaved vegetation or surface debris and receive no subsequent attention from either parent. The adhesive eggs attach loosely to plants or substrate. Published aquarium accounts describe conditioning temperatures around 77 °F and pH around 6 as optimal for bringing fish into breeding condition.
Breeding
Breeding G. maculatus in captivity is rated as very difficult, and successful captive reproduction is uncommon. Published accounts suggest soft, slightly acidic water (pH around 6, temperature 75–79 °F) and a well-planted tank with fine-leaved plants or spawning mops near the surface. A gradual drop in water level combined with frequent small partial water changes with slightly cooler water mimics the onset of the rainy season and may induce spawning.
Eggs are adhesive and small, deposited individually or in small batches among vegetation near the surface. The adults will consume eggs immediately and must be removed after spawning. Incubation time is not widely documented in the hobbyist literature for this particular species; for related hatchetfishes it typically runs 24–48 hours at tropical temperatures. Fry are very small and require infusoria or commercial liquid fry food as a first food before progressing to newly hatched brine shrimp nauplii. Growth is slow and the survival rate of fry is low without good water quality and very fine live food.
In the aquarium
The spotted hatchetfish is an active, shoaling surface-dweller that should be kept in groups of eight or more individuals to reduce stress and encourage natural behaviour. A minimum tank volume around 40 US gal is recommended, with the emphasis on surface area and tank length rather than height. A tight-fitting cover is absolutely essential: this species is an exceptional jumper and will exit an uncovered tank through even small gaps.
Water should be soft to moderately soft, slightly acidic, and warm — pH 6.0–7.0, temperature 72–82 °F, general hardness up to about 15 dH. The fish prefers subdued lighting, surface vegetation or floating plants to provide shade, and a dark substrate that reduces reflections. Flow should be gentle; strong surface turbulence is not well tolerated. Tankmates should be similarly sized, peaceful species that occupy lower water levels — pencilfish, small tetras, dwarf cichlids, and Corydoras are all compatible. Longevity in good conditions is around four years. The spotted hatchetfish is a specialist fish best suited to experienced aquarists comfortable maintaining soft-water chemistry and providing live or high-quality frozen foods.
Conservation
The IUCN Red List assessed Gasteropelecus maculatus as Least Concern (LC) in April 2019, reflecting a range that spans multiple river drainages across eastern Panama, Colombia, and Ecuador, with no evidence of rapid population decline at the time of assessment. The species does not appear on the CARES Preservation Program priority list.
Within its Ecuadorian range, the DePaul University Western Ecuador Fishes project notes that the species has a relatively restricted distribution in the Esmeraldas Province and its status in Ecuadorian national waters was uncertain at the time of that survey. Deforestation and agricultural runoff affecting Pacific-slope drainages in Ecuador and Colombia represent the principal long-term threats to the clearwater habitats the species prefers. The aquarium trade has historically collected hatchetfishes from these regions, though demand for G. maculatus specifically is lower than for the more commonly traded G. sternicla. Aquarists are encouraged to source captive-bred stock when available.