[1] It is contrasted with internal fertilization, in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
[2] In animals, external fertilization typically occurs in water or a moist area to facilitate the movement of sperm to the egg.
[5] Invertebrates utilizing external fertilization are mostly benthic, sessile, or both, including animals such as coral, sea anemones, and tube-dwelling polychaetes.
While in the water, the male and female must both release gametes at similar times in order to fertilize the egg.
[4] To look into the effect of female choice on external fertilization, an in vitro sperm competition experiment was performed.
[6] Benthic sessile animals that make up the majority of invertebrates using external fertilization rely on ambient water motion to bring the sperm and eggs together.
Other invertebrates that externally fertilize are organisms like the sea urchin, are confined to shallow burrows on exposed shores.
[3] Hydrodynamic conditions and gamete properties control the efficiency of fertilization because they influence the rate at which the water mixes.
[3] The presence of food, resources, favorable environmental conditions, and the lack of predators are thought of when thinking of survival of the next generation.
[11] This mass reproductive event is given by reef forming corals, which perform a synchronized release of gametes in one evening from dusk to midnight.
[7] Although fertilization is usually thought of as a short-term process, there is the possibility of gametes being retained on the surface of an animal for an extended period of time.
Females approach the area and listen to all of the different male calls, and then continue to move towards the mate she chooses.
[15] Over the course of a breeding season, males can copulate numerous times by releasing sperm anywhere he finds unfertilized eggs or encounters a female who is/wants to spawn.
[19] To further increase sperm competition, there is a larger thickness to an anuran oocyte gel, specifically the green tree frog.
[21] There are instances where males will create habitats in an attempt to monopolize females and increase their chance of fertilizing eggs.
A decrease in osmolality after spawning in fresh water makes a cyprinid fish's sperm motile.