Hyphessobrycon eschwartzae (ROMÁN-VALENCIA & ORTEGA, 2013)

Hyphessobrycon eschwartzae, also known as the Madre de Dios tetra, is a freshwater fish species found in the Madre de Dios River basin in Peru. It was first discovered in 2008 by German aquarium fish exporter Hans-Georg Evers, and was later described and formally named by Dr. Fernando C. Dagosta in 2010.

Hyphessobrycon eschwartzae belongs to the Characidae family, which is one of the largest families of freshwater fish in the world. This species is small, growing up to 3.5 cm in length, and is known for its striking lateral stripes that run along its body. It has a silver-colored body with a distinctive dark stripe that runs from the eye to the tail, and a red stripe above the dark lateral line.

Hyphessobrycon eschwartzae can be distinguished from other Hyphessobrycon species in the Madre de Dios watershed by its anal fin rays, dentary teeth, premaxillary teeth, and lateral line and dorsal fin scales. It differs from H. loretoensis in having fewer pored scales in the lateral line and fewer scales between the lateral line and dorsal fin. It differs from H. heterohabdus in having fewer lateral scales, fewer pored lateral line scales, fewer predorsal scales, and more maxillary teeth.

Hyphessobrycon eschwartzae is part of the putative H. heterorhabdus-group of closely related species within the genus, which is characterized by a thin, usually dark, lateral body stripe. Lima et al. (2014) proposed a putatively monophyletic H. heterorhabdus-group containing only three species, H. heterorhabdus, H. amapaensis, and H. eschwartzae. These species 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, and upper half of the eye red.

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 color pattern. Weitzman & Palmer (1997) hypothesized the existence of a monophyletic assemblage within the genus based on color pattern and male fin morphology that they termed the ‘rosy tetra clade,’ with one of the characters supporting its monophyly being the presence of a prominent dark marking on the dorsal fin.

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 analyzed 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. pyrrhonotus than to other species in the genus.

In summary, Hyphessobrycon eschwartza is a species of fish that can be identified by the presence of bony hook-like structures on the anal-fin of males. Specifically, males possess 5 pairs of these structures on the fourth simple ray and 6-10 pairs on each of the first three branched rays. Females, on the other hand, lack these hooks and are generally heavier-bodied than males. These physical characteristics are important for distinguishing between male and female individuals of this species.