How Do Fish...REPRODUCE?
Reproduction is different depending on the species but generally happens one of three ways. In most cases, the female drops eggs in the water which are immediately fertilized by sperm from the male. Another way is for fertilization to occur within the females body before she drops them into the water. With the third and final method, the female retains the eggs within her body and the young are born alive. Some sharks and guppies give birth this way.
Nonguarders: Most freshwater fish do not guard their eggs, but scatter their eggs. Trout hide their eggs in depressions or "nests" of stones. The number of eggs a female trout produces is determined by her size. An 8-inch fish may lay only 300 eggs, while the nest of a 12-inch nest may contain 1,000 eggs!
Guarders: Some species of fish such as darters and catfish guard their eggs. Males will chase off predators.
Bearers: These fish carry their young as they develop, either inside the female or outside, often in the mouth of the male. Sharks, rays, molly and gambusia give birth to live young.