1001 Space Earth Nature Evolution Fossils and Prehistoric Life Dinosaurs Simple Animals Insects and Spiders Fish Amphibians Reptiles Birds Sea Mammals Land Mammals Plant Kingdom How Plants Live Unusual Plants Ecology Conservation Animal Behaviour Pets and Farm Animals History Human World Science and Technology	Do all fish lay eggs? Some species, such as the sailfin molly, keep their eggs inside themselves until the young hatch. Then they give birth to up to 200 live young.   Previous: Back Book: 1001 Section: Nature Chapter: Fish