How to Tell When Tetras Have Babies
Tetras are relatively small small fish that come in a variety of colors, including brilliant blues, blacks and reds. They do best in groups, called "schools." Tetras are peaceful fish and do well in community aquariums. Certain tetra species will readily breed in your tank, while others require specific conditions if you want them to spawn. Monitor your aquarium several times a day to see if they are breeding.
Observe the fish's behavior. Males and females in a school of tetras may pair up. Though sometimes difficult to distinguish, females are typically larger than males and more plump around the belly; males have bolder coloration. If you see a male chasing a female and then they are swimming side-by-side, they are most likely in the process of spawning. Tetras are egg-scatterers; the female releases her eggs and they sink to the bottom of the aquarium.
Look for the eggs. These are tiny clear globes; a black dot inside an egg means it was successfully fertilized. If you have Java moss or other plants or have placed a spawning mop at the bottom of your tank, you will see the eggs sticking to the leaves or yarn. Tetras do not care for their eggs and consider them food. Separate the eggs from the fish if you want to the eggs to hatch.
Look for the babies (called fry). Fertilized eggs hatch 48 hours or so after the eggs are released by the female. It takes a few days for the fry to become free-swimming, so look at the bottom of the tank. You should see the tiny fish hovering by their eggs. They will survive on their yolk sacs until they swim about the tank, when they will require regular feedings.