This name is derived from the Greek word akantha, meaning quill or spike, in reference to its spiny body. This specific epithet refers to the Greek god Adonis - a term used these days in referring to handsome youths. Its use here is in reference to the attractive polka-dot colouration of this species during its youth.
The genus can be distinguished from other similar genus by the combination of lack of adipose fin and the well-developed, rough keels along the side of the body. Hard to mistake with any other loricariid other than perhaps Acanthicus hystrix when adult. Quite slender in relation to body length, even delicate in appearance when very small, although as they grow they become much more robust. Small specimens have spots over the whole body, which become bands on the caudal filaments. These spots become relatively smaller and fewer in number with growth, they are reduced to remaining on the caudal peduncle and sometimes on the leading rays of the pectoral fins. Larger adults lack white spots. When adult the pectoral fins can be in excess of 15 cm in length, giving a remarkable front profile. Acanthicus adonis is distinguished from all other congeners in having a juvenile coloration of white spots, a more pointed (vs. rounded) snout, and reduced odontodal growth on the snout margin and the preoperculars. The original description also alludes to additional color differences (pitch black for A. adonis and dark brown for all other Acanthicus).
It is probable that males are more heavily spined over the whole body, including the interopercular region, although this species is so extremely spiny that it would be necessary to compare a number of adult specimens (which very few people have the space for).
Males are also probably more aggressive and active in territorial defence, but this is a particularly combative species regardless of gender.
In such a large species, examination of the genital area is the easiest method of determination.
A superb display fish for public aquaria or the dedicated private aquarist, this species has much to recommend it for those willing to provide it with the space needed to do it justice. Not at all difficult to care for, although care should be taken when buying small fish to ensure that they are healthy, feeding and do not look at all emaciated. Once large they can and do swim actively at all times of the day, and will catch the attention even of non-aquarists with their prehistoric appearance and boisterous nature.
Although described from the Rio Tocantins, this species does appear to have a much wider distribution through the Amazonian region. It is unclear whether it is anywhere sympatric with Acanthicus hystrix. Amazon, Lower Amazon, Tocantins, Lower Tocantins(click on these areas to find other species found there) Amazon(click on these areas to find other species found there)
Very much a generalist or opportunist feeder, this species is happy with most good quality aquarium foods, and will also eat many other foods as offered to other loricariid catfish, from fruit and vegetables through to molluscs, crustaceans and even pieces of fish. They do graze wood, although whether this is a requirement or whether it is just as part of their general grazing is not known.
Robust! Large pieces of bogwood, branch wood etc. are ideal. Rock work should be heavy enough so that an adult fish cannot knock them around, this means nothing smaller than a house brick. The best substrate is by far an inert sand.
To keep more than one individual would require a huge aquarium. A single adult male can easily be the most dominant fish in a 1000 gallon aquarium with other large neotropical fish, and other catfish housed with one need to be robust. There should be ample refuges for all the catfish, as when this fish decides to take one over it will regardless of whether the rightful owner is present or not. Care should probably be taken not to house them with other highly competitive loricariids such as Pseudacanthicus etc., as this is likely to result in serious injuries or death to one or both fish.
One specimen was observed to have killed a very large P. gibbiceps by stripping the skin from the fish when it tried to escape into a refuge that was too small.
Given the filtration demands posed by the feeding behaviour of this species, small fish are probably not a good idea, but no problems were observed when housed with medium-to-large midwater swimming fish such as Pike Cichlids, Aeqidens, Brycon, large Anostomids, Myleus/Mylossoma, Prochilodus etc. etc.
As has already been mentioned however, other Loricariids can suffer, although Panaque seem to be able to anticipate when they are going 'too far' and get out of the way.
They have been bred in captivity, further details will be provided as soon as they are available. It would be fascinating to observe courtship, breeding and care of the fry, but it should probably only be attempted in ponds or huge aquaria. Even in a 1000+ gallon aquarium an adult male would be capable of making the life of a female very unpleasant.
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