This is the best-known of three similar-looking species most commonly-referred to as the 'bleeding heart' subgroup, the other two being H. socolofi and H. pyrrhonotus.
All possess a reddish humeral spot which is not present in any other characid with other shared characters including possession of 6 -14 maxillary teeth, 7-9 scales above the lateral line, 5-7 scales below the lateral line and 26-33 anal fin rays.
H. erythrostigma differs from H. socolofi in the following characters: 33-34 vertebrae, mode 33 (vs. 31-33, mode 32 in H. socolofi); a white longitudinal band extending distally along the majority of the anal-fin in adults, covering 70-95 % of the rays (vs. white band covering 45-50 % of the branched anal-fin rays only); first branched ray of anal-fin longest in adult males (vs. third branched ray); presence of hook-like structures on the anal, pelvic and dorsal fins in mature males (vs. numerous hooks on all fins except the adipose -fin in mature males); absence of such hooks in females (vs. hooks present in the anal-fin of mature females); (scales cycloid (vs. scales cyclo-ctenoid in mature males and some mature females); pelvic-fin of females measuring 19.63-23.83 % SL, reaching tip of 3rd-5th branched anal-fin rays (vs. 15.69-18.88 %, reaching origin of 1st branched anal-fin ray).
It can be told apart from H. pyrrhonotus by lacking (vs. possessing) a red, wedge-shaped patch of red pigmentation in the upper part of the body and the presence (vs. absence) of hook-like structures on the anal, pelvic and dorsal fins in mature males.
Limited genetic analyses have revealed that the bleeding heart group is probably monophyletic, but that there may be more species involved (Paz et al., 2014)[10]. The current concept of H. socolofi appears to represent a paraphyletic taxon, for example, while H. pyrrhonotus also contains distinct lineages, although further work is necessary in order to deduce taxonomic implications.
In addition to forming their own putative assemblage the bleeding heart tetras have regularly been included in the larger 'Hyphessobrycon bentosi' subgroup of the H. callistus group as proposed by Géry (1977). At the time of Géry's work H. erthythrostigma was the only recognised bleeding heart tetra and he considered it to differ from other H. bentosi subgroup members by a combination of morphometric characters plus the red humeral spot.
Weitzman & Palmer (1997) expanded Géry's concept and proposed the existence of a putatively monophyletic assemblage based on colour pattern and male fin morphology that they termed the ‘rosy tetra clade’. It was composed of species with the following shared characters which set them apart from other Hyphessobrycon species: pink to red or reddish-brown body colour; 22-29 branched anal-fin rays; 29-34 longitudinal scales; two sets of teeth on the premaxilla with 1-4 teeth in the outer series and 7-12 in the inner series.
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.
Like many small characids, H. erythrostigma is known to be susceptible to an affliction which causes some or all of the body scales to appear metallic gold in colour. It remains unclear whether this is a consequence of a parasitic infestation, as has been suggested, but affected fish appear to be in no discomfort and their lifespan and overall health seem undiminished.
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