This species is popular in the ornamental trade, although it is sometimes confused with the similar-looking congeners H. loretoensis and H. metae. In particular, it has repeatedly appeared under the name H. metae in aquarium literature.
It can be identified via the following combination of characters as per Géry (1977): elongate in shape with body depth fitting 3.8-3.9 times in its standard length; caudal peduncle narrow, its depth fitting 1.8 times in its length; head short, interorbital broad, snout short and rounded; dorsal-fin insertion anterior to midbody; 9-10 predorsal scales; (8-10) 34-35 lateral scales; caudal-fin red or brownish.
H. loretoensis and H. metae are both less elongate with body depth fitting less than 3.6 times in its standard length and the caudal peduncle depth fitting 1.2-1.75 times in its length, plus their snouts are of moderate length and pointed in shape. H. loretoensis further differs from H. peruvianus in possessing 10-11 predorsal scales, (5-7) 33-34 lateral scales and a bright brick-red caudal-fin, while the dorsal-fin insertion is located at or 'scarcely' anterior to midbody. H. metae has 9-10 predorsal scales, (6-9) 30-31 lateral scales and the dorsal-fin insertion is posterior to midbody.
The three species also exhibit differences in colour pattern; in both H. loretoensis and H. peruvianus there is a broad dark band in the lower portion of the body, between the opercle and caudal peduncle, whereas in H. metae the dark band is prominent only on the caudal peduncle itself. In addition, the dark band extends to the tips of the median caudal-fin rays and there is a bright red marking at the base of both caudal-fin lobes in H. peruvianus, but in H. loretoensis the dark band extends only slightly onto the caudal-fin, which is a more-or-less solid brick red colour. In H. metae the dark caudal peduncle marking continues onto the base of the median caudal-fin rays, and there is a yellow-to-orange marking at the base of each caudal-fin lobe.
All three species are included in the putative H. aghula group of closely-related species within the genus as proposed by Géry (1977, see below) of which members share the following characters which set them apart from other characids: lower half of the body dark, especially above the anal-fin; usually possessing a laterally-elongate humeral spot, more-or-less united with a broad asymmetrical lateral stripe. Other species in this group include H. agulha and H. herbertaxelrodi, although some authors have included one or more of these, including H. peruvianus, in the H. heterorhabdus group.
Lima et al. 2014 noted similarities between the H. aghula group and their revised H. heterorhabdus group which comprises Hyphessobrycon heterorhabdus, H. amapaensis, and H. eschwartzae. This trio all possess: a well-defined, elongate humeral blotch which is continuous with a dark, well-defined midlateral stripe that becomes blurred towards the caudal peduncle; a longitudinal red stripe extending along the body above the midlateral line; upper half of the eye red.
This pattern is different to that presented by several members of Géry’s original H. heterorhabdus group, such as H. vilmae, H. cachimbensis, and H. stegemanni, which possess a continuous, solid dark lateral stripe on the body and no obvious humeral blotch.
Hyphessobrycon was raised by Durbin in Eigenmann (1908) as a subgenus of Hemigrammus, differing from the latter by the absence of scales on the caudal-fin.
The grouping was revised by Eigenmann (1918, 1921) while Géry (1977) created artificial groups of species based on colour pattern, and these definitions are still widely used today, e.g., the H. agulha group, the H. heterorhabdus group, etc. These cannot be considered to represent monophyletic assemblages, however, and their concepts continue to be redefined.
Weitzman & Palmer (1997) hypothesised the existence of a monophyletic assemblage within the genus based on colour pattern and male fin morphology that they termed the ‘rosy tetra clade’, with one of the characters supporting its monophyly being presence of a prominent dark marking on the dorsal-fin. This assemblage, plus other morphologically similar species, is considered to represent Hyphessobrycon sensu stricto by some authors, with the remaining species included in a much-expanded H. heterorhabdus group.
Others have proposed conflicting, typically more restricted, views of both the genus and/or its constituent species groups, and significant confusion remains. What is clear is that, as currently recognised, Hyphessobrycon is a polyphyletic lineage containing several genera.
The process of splitting it up has already started, and Malabarba et al. (2012) revalidated the genus Ectrepopterus Fowler, previously considered a synonym of Hyphessobrycon. They also analysed its relationships within the Characidae in the context of Mirande's (2010) previous work, but included the type species, H. compressus, for the first time in such a study. The results demonstrated that H. compressus is more closely-related to 'rosy tetra' representatives such as H. eques, H. pulchripinnis, and H. socolofi than other species then placed in the genus, including Psalidodon anisitsi, H. bifasciatus, H. elachys, H. herbertaxelrodi, and H. luetkeni.
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