When visiting a local fish shop (Belgium), following species was found on sale as Phractocephalus Spec..
Evidently (owning 2 South-American RTC myself) this is by far not a Phractocephalus. The Shop owner could be of no assistance, and put the name he received from the fish provider.
Can anyone shed a light on what these are ?
Below two bad-quality images

Since price can sometimes be of some help, these juveniles (approx 8cm or 2.5") are on sale for around 19 euros (which is about the same amount when expressed in US dollars)
Kind rgds,
Franky