Generally speaking, female Neon Tetras are plumper than males, which causes the characteristic blue streak of this species to appear bent (whereas it will appear straighter on the more slender males). Differentiating between male and female Neon Tetras is easiest when females are in season to breed, since their eggs significantly increase the size of their bodies.
It is necessary to identify males and females if seeking to breed Neon Tetras.
Another consideration for breeding Neon Tetras is to identify only healthy adult fish for the purpose. When Neon Tetras are too old or unhealthy, it is not recommended to breed them, since their young are likely to be of a lower quality.
Once a pair of healthy adult male and female specimens have been identified for breeding, they should be placed alone in a tank with a plentiful supply of live food, such as mosquito larvae.
Light levels in the tank should be gradually increased from darkness until the fish begin to spawn, at which point they should be kept at a constant. This is because the eggs of Neon Tetra may be negatively affected by too much light.
It may also be useful to allow the nitrate content of the water to reach relatively high levels before replenishing upwards of half the tank, since this has been known to help induce spawning.