Which of the following groups is known to reproduce by spawning?

The correct answer is that fish are known to reproduce by spawning. Spawning is a method of external fertilization commonly observed in aquatic animals, particularly in fish. During this process, fish release eggs and sperm into the water, where fertilization occurs outside the body. This reproductive strategy takes advantage of the aquatic environment, allowing for a large number of eggs to be fertilized in a short amount of time, which increases the chance of offspring survival.

In contrast, while birds and reptiles do lay eggs, they typically engage in internal fertilization, where fertilization occurs inside the female's body before the egg is laid. Mammals, on the other hand, give birth to live young or lay eggs in the case of monotremes, but they do not reproduce via spawning. Therefore, the process of spawning is specifically associated with fish, making it the clear choice among the options presented.