Fish breed in a number of different ways. Most lay eggs but some give birth to live young. In freshwater fish, the fertilized eggs usually sink to the bottom or are sticky and therefore stick to plants or rocks. In some species (such as tilapia) the eggs may be collected by the adult fish and held in the mouth by the female after fertilization. The eggs hatch in the parent’s mouth and the young develop there until they are large enough to be released. These fish practice a high degree of parental care,
which means that large numbers of young can be successfully reared and protected without being eaten by other fish. Female livebearers (such as guppies) may store sperm for months, which they can use to fertilize their eggs when males are not available. The baby fish develop inside the mother and when she gives birth to the babies they are able to feed and look after themselves.
Before fish will breed they must be in good condition. They should be in an environment that is beneficial for
spawning (e.g. the correct temperature, plants for egg attachment, etc.). They should also have been eating the correct food which helps make good-quality eggs