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Several Brachyrhamdia species have developed colour patterns that mimic syntopically-occurring Corydoras spp. throughout the life-cycle, and the remainder may mimic Otocinclus or smaller Corydoras spp. when juvenile. Among other catfishes they're closely-related to members of the genus Pimelodella, but differ in...

Collected from small streams flowing through savanna grassland containing clear, light brown-coloured water with substrates of sand and gravel and little in the way of submerged or riparian vegetation. At the type locality pH varied between 5.8 – 6.3, GH and KH were both <1°, conductivity was 9-13 μs and temperature 24.7 – 27.2°C/76.6 – 80.1°F.

It was initially going to be described as Hyphessobrycon cardinalis by Myers and Weitzman (1956) but just before this was due to be published Schultz presented an alternative description in the hobbyist magazine 'Tropical Fish Hobbyist' and named the fish after the publication's founder, Dr. Herbert R. Axelrod. A significant proportion of the fish available in the aquarium trade are still wild caught or derive from community-led breeding projects such as Project Piaba in the middle Negro region, where this sp...

A number of sources state that S. brandtii can be identified by the relatively anterior position of the anal-fin origin beneath the first few dorsal-fin rays. However, images of specimens collected from the rio São Francisco, where it is the only member of the genus present, suggest that this is not always the case and this is also supported by the figure from Eigenmann (1915). No recent diagnosis of the species is available.

Following Fink (1993), P. piraya can be distinguished from congeners by the following combination of characters: adipose fin with rays in larger specimens (vs. always without rays in other Pygocentrus species); branched dorsal-fin rays 15-18, usually 16 (vs. 14-18, usually 15); usually 7 neural spines anterior to first pterygiophore (vs. usually 6); vertebrae 36-39, usually 38 (vs. 35-38, usually 36). It can also be identified by colour pattern since it possesses distinctive bright yellow-orange pigmentation on the lower jaw, opercle and lateral body in life.