Petitella

The firehead tetra, Hemigrammus bleheri, is a characin from blackwater rivers of the Rio Meta and Rio Negro in Colombia and Brazil. Most fish sold as the 'rummy-nose tetra' are this species. Of the three look-alikes, with H. rhodostomus and Petitella georgiae, only H. bleheri has red extending beyond the gill covers, although the red fades in fish in poor condition. Bittencourt et al. (2020) proposed moving it to Petitella. It should be kept in groups of 10 or more.

The false rummy-nose, Petitella georgiae, is a small tetra from the Rio Purus in Peru and Brazil and the Rio Negro and Rio Madeira in Brazil. This is one of three very similar species commonly sold as 'rummy-nose tetra', and the lack of a dark blotch at the bottom of the caudal peduncle is one way to separate it from the other two. One of the more tightly shoaling small tetras, it needs a group of at least ten.

The rummy-nose tetra, Hemigrammus rhodostomus, is a characin from blackwater rivers of the Rio Orinoco and lower Amazon basin in Venezuela and Brazil. This is the 'real' rummy-nose. Most fish sold under the name are the firehead tetra, H. bleheri, and the 'false' rummy-nose, Petitella georgiae, is also very similar. The head colour, the caudal peduncle blotches and the line from the central caudal band separate the three. Bittencourt et al. (2020) proposed moving it to Petitella.