How do fish reproduce?
      Fish breed in different ways. There are two main strategies that fish use: egglaying and livebearing. Livebearing female fish are internally fertilized by the male fish, and carry the fry for about a month before delivering them. Egglaying fish lay eggs instead of giving birth to little fish.
     Egglayers have many methods of laying eggs. For example, substrate spawners lay eggs in protected areas such as plants, rocks, wood. Mouthbrooders actually keep their eggs in their mouths until the eggs hatch.  

What is the structure of fish?