Astyanax aeneus, the banded tetra, is a small species of fish native to southern Central America and northern South America. It can be found in a variety of environments, including lakes, rivers, ponds, and slightly brackish locales like lagoons. As well as a varied habitat, it has a varied omnivorous diet: algae, seeds, leaves, insects, and fish fry appear to be the most common. The IUCN considers A. aeneus a species of least concern, given its widespread habitat and hardy nature. Various threats throughout its range appear to have little impact on overall survivability. Despite a comparatively-short reproductive period, individuals also demonstrate high fecundity, which assists in maintaining a stable population. Description Astyanax aeneus has silver sides, a white belly, and a greenish-brown back. There is a black rhomboidal shape on the caudal peduncle that extends to the tips of the middle caudal rays, but the fins are mostly transparent otherwise. Occasionally, the dorsal and caudal fins will display some red or yellow coloration. Upon preservation in alcohol, a gray band develops from the humeral spot to the caudal blotch; the humeral spot itself is distinct in living and deceased specimens, and is sometimes rhomboid or P-shaped. Occasionally, there may be the suggestion of a second spot behind the first on both sides, but this is often just an intensification of the lateral stripe located there, and is not a true second humeral spot. The snout is blunt, and the mouth opens forward (as opposed to being upturned). The eye is almost half the size of the head, and is most often wider than the snout is long. Body depth is intermediate, ranging from 34 to 39% SL in larger specimens. Notable morphometric characteristics include 9–11 dorsal-fin rays, 22–31 anal-fin rays (modally 25), and 10–11 pectoral-fin rays. A. aeneus is equipped with gill rakers for feeding, and southern populations may have a higher number of rakers than northern. Sexual dimorphism Astyanax aeneus demonstrates notable sexual dimorphism. Females are the larger sex, reaching 12.0 cm (4.7 in) standard length (SL), while males reach 7.5 cm (2.9 in) SL. As well as this, there are serrations on the maxillary bones of some large males, which is a feature also seen in some congeners. Furthermore, males are more common than females, with a ratio of 1.8:1 males:females. Occasionally, nuptial tubercles (small fleshy extensions on the anal or pelvic fins of male specimens) may