Wild populations vary in colour pattern depending on origin, and some populations have previously been described as distinct species.

A form from Peru has a particularly silvery body colour, for example, while another, marketed as ‘super red’ possesses an unusually long red stripe on the body, extending much of the length of the dark central stripe. A population from around Boa Vista in the rio Branco system, Pará state, Brazil has an ocellus o…

This species has been referred to the genera Poecilobrycon and Nannobrycon in the past and in the aquarium hobby is also known as ‘rocket’, ‘brown’, ‘brown-tailed’, ‘diptail’, or ‘tubemouth’ pencilfish.It’s a popular aquarium fish and has an interesting oblique swimming-style, a behavioural trait shared only with N. unifasciatus among congeners.

In the original description the colour pattern is given by Steindachner as a brown lateral stripe exte…

Localities known in the hobby include ‘Pastaza’, ‘Putumayo’, ‘Requena’, ‘Río Nanay’, ‘Rio Napo’, ‘Maniti’, ‘Momón’, ‘Río Tigre’, ‘Río Ampiyacu’, ‘Shishita’, ‘Shushupi’, ‘Yavari’, ‘Tefé’, ‘Manaquiri’, ‘Lago do Januari’, ‘Mamori’ (often misspelled ‘Mamuri’), ‘Careiro’, ‘Manacapuru’, ‘Juruá’, ‘Curuaí’, and ‘Purutu’ though we’ve been unable to find anywhere matching the latter name within the species’ known distribution, and in fact several of these names are applied incorrectly on a regular basis.

This is the type species of the genus Aequidens and has the widest distribution of any member species. It exists in various colour forms depending on locality with variants from Ecuador and Peru being particularly sought after since they develop striking red (Ecuador) or orange (Peru) colouration on the lower part of the jaw, head and anterior portion of the belly whereas those from Brazil tend to have an overall grey/blue/green colouration, for example.

Despite its type status it's long…

In the Amazon region it is only specimens larger than around 160 cm and werighing in excess of 50 kg that are referred to as ‘Piraíba’ with the name ‘filhote’ normally applied to smaller individuals. Other vernacular names include ‘Salton catfish’, ‘Kumakuma’; and ‘tiger antenna catfish’; with members of the genus often referred to collectively as ‘goliath catfishes’.

A. bimaculatus is not a popular aquarium fish but is available on occasion exception, most often as a contaminant among shipments of other species.

It’s identity is also in question to an extent with the name currently applied to what is considered to represent a species complex comprising at least four taxa.

The majority of records pertain to the rio Guaporé (Río Iténez in Bolivia), the main affluent of the rio Mamoré, which drains the vast tropical wetland known as the Pantanal, and the upper rio Paraguai, which also has its headwaters in the Pantanal but flows in the opposite direction. The Guaporé and Paraguai are connected due to rising water levels during the annual wet season.

It exhibits slightly different behaviour to the majority of congeners in that it tends to swim in midwater and spends a large proportion of its time away from the substrate. Its morphology exhibits corresponding adaptations towards a pelagic existence with a relatively large eye, a more terminal mouth position, more strongly-forked caudal-fin, and more symmetrical body shape than most other Corydoras species.

The congener C. seussi, which is also native to the rio Mamoré, has a similar colour pattern but its snout is noticeably prolonged compared with that of C. gossei, plus there are some subtle differences in pigmentation. There is a third variant which has been referred to as ‘CW069’ in the aquarium hobby and appears to be somewhat intermediate, with a short, rounded snout as in C. gossei but a colour pattern more reminiscent of C. seussi.