Taxonomy & naming
Mimagoniates barberi was described by Charles Tate Regan in 1907. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) lists Mimagoniates barberi Regan, 1907 as the valid name; the authority is not parenthetical because the species was described in Mimagoniates, where it remains today.
The genus Mimagoniates belongs to the tribe Glandulocaudini within the family Characidae. Glandulocaudines are a neotropical group of small characids that share a specialised caudal gland apparatus in males, believed to disperse pheromones during spawning. Mimagoniates is the largest genus in the tribe and includes several species distributed across Atlantic Forest river systems in Brazil, Paraguay, and Argentina. M. barberi is one of the more widely kept species in the hobby and the one most frequently associated with the 'croaking tetra' common name, though the sound production characteristic applies to some degree across the genus.
Morphology
Mimagoniates barberi is a slender, elongate characid reaching a maximum of about 1.5 in total length according to FishBase. The body is fusiform and laterally compressed, typical of the genus, with a pointed snout and a relatively large eye. The overall colouration is translucent silver to pale blue-grey, often with a faint iridescent blue or greenish lateral sheen depending on light angle. A thin dark lateral stripe runs along the mid-body from behind the eye toward the caudal peduncle.
Males are distinguishable from females by the presence of a well-developed caudal gland — a modified tissue structure in the caudal fin base — and by their slightly more slender build. Females are typically deeper-bodied when gravid. Both sexes may show a faint orange to yellow tint in the fins, and males in breeding condition can flush more intensely. The caudal fin of males is modified, with some rays extended or otherwise differentiated, associated with the gland function.
Habitat
Mimagoniates barberi inhabits streams, small rivers, and flooded areas within the Atlantic Forest biome of south-eastern South America, primarily in southern Brazil (states of Paraná and Santa Catarina), Paraguay, and north-eastern Argentina. These are typically cool to warm clear-water streams with moderate flow, substrates of sand, gravel, or leaf litter, and margins with overhanging or emergent vegetation.
Atlantic Forest streams in the species' range tend to be soft and acidic to near-neutral, reflecting the predominantly granitic and sandstone catchments of the region. Water temperatures in upland and mid-elevation Atlantic Forest streams span a wide seasonal range, often dropping considerably in austral winter, and the species is more cold-tolerant than many tetras of tropical origin. Mimagoniates barberi typically occupies the upper and middle water column in areas with some cover, often near the stream surface under overhanging bank vegetation.
Feeding
Mimagoniates barberi is an insectivore-leaning omnivore in the wild, feeding primarily at or near the water surface on small invertebrates including aquatic and terrestrial insects, insect larvae, and microcrustaceans such as small Daphnia and Cyclops. The species is an active, visually oriented feeder and tends to take prey from the surface film or the upper water column.
In the aquarium it adapts well to small prepared foods — fine flake and micro-pellets — but thrives with regular offerings of live and frozen invertebrates: Daphnia, cyclops, brine shrimp nauplii, and micro-worms all elicit strong feeding responses and help maintain condition. Given its small size, food particle size matters; items should be appropriately fine. Good diet variety supports coloration and reproductive condition.
Mating
The courtship behaviour of Mimagoniates barberi is among the most remarkable of any small characid. Displaying males produce an audible croaking or clicking sound, generated by rapid movements of the pectoral fin base against the body wall; this sound production gives the species its common name. Males also actively release chemical signals via the caudal gland, fanning the modified caudal fin to disperse pheromones toward females. Together, the acoustic and chemical signals form an unusually multimodal courtship display for a fish of this size.
Males establish loose display territories and pursue females persistently. Spawning is of the egg-scattering type: pairs move together briefly and release eggs and milt without tight adhesive embrace. The croaking is most frequent and intense during active courtship and subsides once spawning is complete. Keeping multiple males together intensifies display and helps ensure females are regularly courted.
Breeding
Mimagoniates barberi is an egg-scattering open spawner with no parental care. Eggs are small and semi-adhesive, typically deposited among fine-leaved plants, moss clumps, or synthetic spawning mops in the upper part of the water column. Adults will consume eggs if given the opportunity, so breeders either remove spawning medium to a separate container or move adults out after spawning activity is observed.
Breeding is most reliably triggered by keeping well-conditioned groups at slightly cooler temperatures — the species' Atlantic Forest origin means it tolerates and may be stimulated by temperatures in the low-to-mid 20s Celsius. Eggs hatch within a few days at typical breeding temperatures. The tiny fry are free-swimming shortly after hatching and require very fine first foods such as infusoria or commercial fry preparations before graduating to newly hatched brine shrimp nauplii. The species is regularly bred in captivity and captive-bred stock is available in the trade.
In the aquarium
Mimagoniates barberi is a peaceful, active schooling fish suited to smaller aquaria given its diminutive size, though a group of eight or more in a tank of at least 23.5–29.5 in length allows the full social and courtship repertoire to be observed. The species does best in a setup that mimics its Atlantic Forest stream origins: soft to moderately hard, slightly acidic to neutral water, temperatures in the range of 64–79 °F (64–79 °F), and good surface oxygenation with some flow.
Its cold tolerance makes it compatible with subtropical species and suitable for unheated tanks in temperate climates during warmer months. Planting along the back and sides with open surface swimming space suits its habits; fine-leaved plants or spawning mops double as breeding substrate. The croaking courtship display is best observed in a quiet room — the sound is soft but clearly audible when the aquarium is close by. Tankmates should be small and peaceful; the species can be outcompeted at feeding by larger or more assertive fish. It is generally hardy once established, though it benefits from stable water quality and cooler temperatures than many tropical tetras.
Conservation
No IUCN Red List assessment for Mimagoniates barberi was available at the time this article was prepared. The species inhabits Atlantic Forest stream systems, one of the most threatened biomes on Earth: the Atlantic Forest has been reduced to a small fraction of its original extent through centuries of deforestation, agriculture, and urban expansion across coastal Brazil and adjacent countries. Stream species endemic to or concentrated in this biome face ongoing habitat pressure from catchment degradation, water extraction, and pollution.
Mimagoniates barberi's moderately wide distribution across southern Brazil, Paraguay, and north-eastern Argentina gives it a broader range than many strictly endemic Atlantic Forest taxa, which may buffer it against the most severe local impacts. Captive breeding is well established, and the species is widely available in the trade as tank-bred stock, which reduces any pressure that collection might place on wild populations. Monitoring of the Atlantic Forest stream fish community as a whole remains a conservation priority given the pace of ongoing habitat loss in the region.