Final answer:
External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water during the process of spawning.
Step-by-step explanation:
External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water.
After the sperm reaches the egg, fertilization takes place.
Most external fertilization happens during the process of spawning where one or several females release their eggs and the male(s) release sperm in the same area, at the same time.
The release of the reproductive material may be triggered by water temperature or the length of daylight.
Nearly all fish spawn, as do crustaceans (such as crabs and shrimp), mollusks (such as oysters), squid, and echinoderms (such as sea urchins and sea cucumbers).
Frogs, corals, squid, and octopuses also spawn.