Mexican Tetra Identification Guide

Key identification features

• Small, laterally compressed, silvery body about 7-9 cm long with an olive-green to blue sheen on the back
• A faint dusky vertical bar or dark smudge just behind the gill cover
• A distinct dark spot at the base of the caudal fin, often bordered by pale edges
• Deeply forked tail and a single small adipose fin between the dorsal and tail
• Large eyes and a slightly upturned mouth typical of surface-feeding tetras

Common look-alikes

• Blind cave tetra: the same species' cave-dwelling form, told apart instantly by its lack of functional eyes and near-total loss of pigment
• Other silvery river tetras or shiners: separated by the Mexican tetra's caudal spot and adipose fin, which many shiners lack
• Serpae tetra: has a solid red-orange body rather than silvery flanks, ruling out confusion at a glance

Where you'll see one

Native to fast streams, rivers, and springs from central Texas and New Mexico south through the Rio Grande basin into central Mexico, this hardy tetra tolerates a wide range of temperatures and often schools in open water near vegetation or rocky pools.