The three species called 'rummynose tetras' can be hard to identify, but I would say these are most likely Petitella rhodostoma (syn. Hemigrammus rhodostomus). The presence of a dark spot on the ventral edge rules out Petitella georgia, and the black stripes on the tail are too thin to be Petitella bleheri (syn. Hemigrammus bleheri)
