Sexing is quite easy, adult females are stockier, and a little larger than males. The swimbladder of males is pointy towards the front, while females have a rounded swimbladder.

X-ray tetra is easy enough to spawn, but raising the tiny fry can be harder. For breeding a small 20-30 litres separate tank is enough that should contain a few clumps of fine-leaved plants, such as java moss where the fish can deposit their eggs. Another solution to put some kind of mesh with a large enough grade to the bottom of the tank so the eggs can fall through it and can protect the eggs from the adults. The aquarium water should be soft (1-5 dGH), slightly acidic (pH 5,5-6,5) with a temperature of 27-29 °C. Filtering the water through peat is useful. They can be spawn in pairs or in a small group, but either way Feed the adults with plenty of live and frozen foods to bring them into good condition. Place the adtult fish into the breeding tank in the evening, and they will usually spawn the following morning. The parents will eat the eggs, so after spawning they should be removed from the tank. The 300-400 eggs which are laid on the fine-leaved plants will hatch in 24-36 hours, with the fry becoming free swimming a 3-4 days later. The tiny fry can be fed with very small live foods or with liquid fry food for the first days, until they are large enough to accept brine shrimp nauplii. Both eggs and fry are light sensitive in the early stages of life and the tank should be kept in darkness. Six weeks old fry start to show adult coloration.