Taxonomic confusion is rife in the literature dealing with Metynnis species. There are 28 nominal species and only 16 are recognized as valid. The elevated number of synonyms is probably a consequence of the enormous variability of body shape and color pattern, which in turn are highly influenced by ontogeny and sexual dimorphism (Zarske & Géry, 1999; Jégu, 2003; Pavanelli et al., 2009; Ota et al., 2013; Ota et al., 2016).
The taxonomy of the genus is still confused and impeded by high ontogenetic variability and sexual dimorphism that includes the presence versus absence of the anal-fin lobe, the elongation of the first dorsal-fin rays, and variation in body coloration (Zarske & Géry, 1999; Pavanelli et al ., 2009; Ota et al ., 2013).
M. fasciatus was initially described as a distinct species by Ahl in 1931, but the loss of the type specimens caused later biologists to question whether this was a valid species or the type specimens had been juveniles of another species (which do show stripes, at least sometimes). Zarske & Gery (1999) sorted this out and confirmed the distinct species.
The photos above would seem to be M. fasciatus.