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.

This species is very similar to Hemiancistrus subviridis in appearance and the two occur sympatrically in nature, although B. demantoides is less common in the aquarium trade. Both have been marketed under the DATZ code L200 with B. demantoides sometimes referred to as ‘L200 high-fin’ or ‘L200a’, the former name in reference to its comparatively long dorsal-fin spine (average length in the type series 42.1 mm vs. 34.3 mm in H. subviridis).

Prior to description this species was traded under the DATZ code L239. It can be distinguished from other species in the genus and other hypostomines (see below for definition of this grouping) by its uniformly black to brownish body and fin colouration with a turquoise to bluish sheen, and the acutely bent shape of midventral body plates 3-5 which form a distinctive keel running along the body, above the pectoral fins…

This species differs from all other described members of the genus by the presence of dark blotches at the dorsal and ventral base of the pectoral fins. Three very similar-looking fishes have been assigned the codes A106, A107 and A108 under the DATZ system and are also known in the aquarium hobby as A. sp. ‘rotpunkt’ (this form has been in the hobby for decades with its precise origin unclear), A. sp. ‘rotpunkt Orteguazas’ (the paratype form of A. alacrina) and A. sp. ‘rotpunkt Guayas’, respectively. It remains to be seen whether they’re conspecific with A. alacrina or not since they exhibit some differences in colour pattern and morphology.

The German term 'breitbinden' translates literally as "broad-banded" and refers to the uniformly broad suborbital stripe seen in males of this 'species' which remains undescribed despite being known in the aquarium hobby for several decades. It's often imported as bycatch among shipments of wild-collected A. iniridae.

Some of the populations have also been assigned th…

Populations known in the aquarium trade include ‘Cuao’, ‘Orinoco’, ‘San Antonio’, and ‘Sipapo Ventuari’.

B. wavrini and its congener B. cupido can be separated by body shape and position of the dark blotch on the posterior portion of the flank. In B. cupido the body is relatively compact and the blotch located above the upper lateral line, whereas in B. wavrini the body is noticeably elongate and the blotch on or below the upper lateral line.

Apparently this species is polymorphic with body patterning varying significantly depending on locality. Individuals collected from black water habitats tend to be noticeably darker in overall colouration, for example, with this being particularly evident among populations from the Guiana Shield.

The genus Ageneiosus was at one point classified in…

This species is a member of the putative A. nasutus group of closely-related species within the genus alongside A. nasutus, A. maculipinna and A. isalineae.

These are characterised by possession of two dark, longitudinal stripes, one running from the tip of the snout to the base and the other from the posterior edge of the lower maxilla to the underside of the caudal peduncle.

An obligate piscivore capable of consuming quite large prey in relation to its body size although it tends to focus on smaller prey such as tetras and related species.

Newly-imported specimens may refuse to accept anything but live fishes although most can be weaned onto dead alternatives once they recognise them as edible, and some even learn to accept dried foods.

The genus Ageneiosus was at one point classified in the family Ageneiosidae alongside the genus Tetranematichthys, but this was not accepted by all authors. The grouping remains poorly-studied with the last major revision having been conducted by Watson (1990) in his unpublished dissertation, in which A. inermis was included under the currently synonymous name A. brevifilis. It can be separated from the majority of the genus (except A. marmoratus) by possession of a truncate caudal fin, and from…