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.

The only other described member of the genus native to southwestern India is B. sharavtiensis which occurs a little further north than B. travancoria in Karanataka state. The two are easily distinguished by colour pattern in that B. travancoria possesses a darkish midlateral stripe and a poorly-defined, but normally visible, post-opercular spot, whereas B. sharavtiensis has no such mark…

Batasio havmolleri (Smith, 1931) is currently considered a junior synonym of B. fluviatilis.

Members of the genus Batasio are characterised by the following combination of characters; laterally-compressed body shape; presence of large sensory pores on the head; a narrow mental region; a pair of prominent posterior proces…

Batasio spp. are obligate inhabitants of headwater streams and the upper reaches of smaller rivers characterised by shallow, fast-flowing, highly-oxygenated stretches of riffles and runs broken up by pools or cascades in some cases. Images of the Ataran correspondingly depict flowing sections of forest-shaded, seemingly well-oxygenated headwaters containing clear water, a mixed sand/rock substrate and lots of submerged driftwood/leaf litter.

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…

The vernacular name ‘lancer’ is derived from the extended dorsal spine possessed by several members of the genus, which currently contains 7 species. B. obscurus is diagnosable from congerners by the following combination of characters: mouth opening relatively small and narrow; oral dentition significantly reduced; dorsal-fin spi…