Middle School Life Science: Fishes, Amphibians, and Reptiles - Fish — Flashcards

A fish is an aquatic, craniate, gill-bearing animal that lacks limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups.
Almost all fish have sexual reproduction, generally with separate sexes. Each fish typically produces large numbers of sperm or eggs. Fertilization takes place in the water outside the body in the majority of fish. Most fish are oviparous. Embryos develop in eggs outside the mother's body.    
In many species of fish, reproduction includes spawning. Spawning occurs when many adult fish group together and release their sperm or eggs into the water at the same time. Spawning increases the chances that fertilization will take place. It typically results in a large number of embryos forming at once. This makes it more likely that at least some of the embryos will avoid being eaten by predators.    
With spawning, fish parents can't identify their own offspring. Therefore, in most species, there is no parental care of offspring. However, there are exceptions. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding.    
Fish eggs hatch into larvae. Each larva swims around attached to a yolk sac from the egg. The yolk sac provides it with food. Fish larvae look different from adult fish of the same species. They must go through metamorphosis to change into the adult form.