Aphyocharax alburnus

Aphyocharax pusillus has a maximum standard length of 6.4 cm (2.5 in). This species and A. avary have been regarded as synonyms but a 2018 study found that A. avary was a valid species. They both differ from all other species within Aphyocharax by having dark brown or black rays in the middle of the caudal fin. It can be distinguished from A. avary by the possession of a smaller number of teeth on the maxilla which are distributed along the proximal half of the bone, compared to a greater number of teeth which are spread along two thirds of the maxillary extension. In this species there is an indistinct humeral spot, a spot to the rear of the operculum, in larger specimens, absent in smaller individuals, whereas in A. avary this spot is typically distinct and clearly discernible.

Aphyocharax pusillus is found in the Amazon basin of Peru, Ecuador, Colombia, Bolivia and Brazil, but the true distribution of this species is unclear due to the confusion between this species and A. avary. Fishes in the genus Aphyocharax are typically very common in middle-sized to large rivers in stretches with sand bottoms and shallow water. This species was recorded in Bolivia in a white water stream which drained from a floodplain lake in Peru. This stream has shores and beds that are sandy/muddy and with a large amount of submerged logs and leaves, a fast current, no aquatic vegetation and gallery forest along parts of its banks.

Aphyocharax pusillus is the type species of the genus Aphyocharax. This name prefixes aphyo, derived from the Greek aphýē, which means "small fry" , referring to the small size of A. pusillus, onto the genus name Charax. Charax means the pointed stake of a palisade, an allusion to the densely set sharp teeth, and is commonly used as a root for characin genera. The specific name, pusillus, means "very small", an allusion to the small size of this species.