The neon tetra is a popular tropical freshwater aquarium fish. This colourful little fish is hardy and readily available. The inexpensive neon tetra is popular with both novice and advance aquarists alike. This social species always adds both colour and movement to an aquarium. The neon tetra is small and peaceful and therefore suitable for the majority of community aquariums. These small fish are not immediately easy to sex, but with practice, an aquarist can learn to tell the differences between male and female fish.
Keep a small school of neon tetras together. Neon tetras are not always easy to sex, but by watching the fish interact with each other, you will find it easier to sex them correctly.
Replace half of the aquarium water with fresh water, as this will induce the neon tetras to begin spawning.
Feed live food, such as mosquito larvae and brine shrimps, at this time. Live food will also encourage the fish to begin spawning.
Observe the fish during the early morning, as this is typically the time they begin to spawn.
Look out for the fish that is performing a dance around another. The fish which is actively displaying is a male. This fish will also chase the female through the aquatic plants in the aquarium.
Turn on the aquarium light so that you can see the tetras clearly.
Look closely at the fish. Those individuals will rounded bellies, are female. This full-bodied look is caused by the eggs that have developed within the female.
Observe the horizontal blue stripe that runs along the flank of the fish. This line is straight in male fish and bends slightly in the females. It is the rounded flanks of the female that causes this colour stripe to bend, but the phenomenon assists the aquarist to sex this species of fish.
Look for egg lying. The fish which is laying is female. Once she had deposited her eggs onto aquatic plants and other decor in the tank, the male swims over the eggs and deposits his milt or sperm over them.
Sex the black tetra exactly in the same manner as you have sexed the standard neon tetra. Both male and female black tetras will darken in colour during the breeding period, so you can not use this characteristic to tell male fish apart from female fish.