Type locality is given simply as ‘Amazon River, Brazil’ and according to current thinking this species has a huge natural range encompassing the Amazon River system in Brazil and Peru plus the Paraná-Paraguay drainage in southern Brazil and Paraguay and rio São Francisco basin in southern Brazil.

Specimens in our images were collected fro…

In the upper Iténez it most commonly inhabits riparian zones with sandy substrates or edges of sand banks, although it’s also been collected in smaller streams and residual flood waters.

It typically forms large aggregations of up to several thousand individuals and at the confluence of the ríos Paraguá and Iténez occurs sympatrically with the congener C. paragua.

This species can be confused with three similar-looking fishes of uncertain taxonomic status which have been assigned the C numbers C024, C077, and C109 in the aquarium hobby.

C024 and C109 are unlikely to be conspecific in that they occur in Pará state, Brazil, several thousand kilometers outside the range of C. acutus, in the rio Guamá (Tocantins drainage), and lower rio Xingu, respectively.

Native to the central Amazon basin with records existing from the Madeira, Branco, Trombetas, and Tapajós river drainages, plus the Rupununi basin in Guyana. Although an affluent of the rio Essequibo and thus not officially part of the Amazon basin, the latter is connected to the rio Takutu, a tributary of the upper rio Branco, during the annual wet season.

Type locality is given by Fowler as ‘Rio Madeira about 200 miles east of W. Long. 62°20′, Brazil’.

Several Brachyrhamdia species have developed colour patterns that mimic syntopically-occurring Corydoras spp. throughout the life-cycle, and the remainder, including B. meesi, may mimic Otocinclus or smaller Corydoras spp. when juvenile. They’re easily told apart from Corydoras by their significantly longer barbels and lack of scute-like plates on the body.

This rich feeding ground is exploited until the sea water returns, at which point the catfishes begin to migrate upstream in massive numbers, moving up the Amazon and its tributaries. Sexually mature individuals are not normally recorded during these events so they’re thought related to feeding and dispersal rather than spawning. The fish are subject to intensive capture by commercial and artisanal fishing operations during this upstream movement.

This species can be told apart from the very similar-looking congener B. filamentosum by its smaller adult size (B. filamentosum can grow to almost 3 m in length), shorter maxillary barbels (never extending beyond base of adipose fin (vs. extending beyond base of adipose fin), moderately-forked with lobes of equal size (vs. deeply-forked caudal fin with upper lobe usually longer than the lower) and body col…

Study of B. rousseauxii has revealed that sexually mature adults are found only in the western Amazon, with no mature individual ever recorded east of Manaus despite the intensive commercial fishery operating there. The total distance covered by some populations during migration from the delta was as much as 5500 km, making it the longest known in any freshwater fish species.

Found in a number of habitat-types, though rarely in smaller tributaries, generally preferring deeper, flowing channels through which it travels for considerable distances at certain times of year. Like other large, migratory pimelodids these movements are typically associated with nutrient-rich, white water drainages rather than nutrient-poor black waters.

This species is assigned the code A188 under the DATZ system and is also known by the trade names A. sp. ‘Inca/Inka’, A. sp. ‘Inka 50’, A. sp. ‘highfin nijsseni’, A. sp. ‘Nijsseni 2’, A. sp. ‘red crescent’ or A. baenschi ‘Inca’.

It’s among those members of the genus produced on a commercial basis and is regularly available in the aquarium trade.