Do fish primarily use internal or external fertilization for reproduction?

Fish primarily use external fertilization for reproduction, which involves the female releasing eggs into the water while the male simultaneously releases sperm over the eggs. This method allows for a large number of gametes to be disseminated in a relatively short time. It is particularly effective in aquatic environments where water currents can help disperse the sperm and increase the chances of fertilization.

Most fish species engage in this form of reproduction, as it often aligns with their life history strategies, allowing for higher reproductive output while relying on the environment, such as water bodies, to facilitate the mating process.

While some fish species do exhibit internal fertilization, this is less common and typically occurs among specific groups that have adapted to different ecological niches. The option of fission refers to a form of asexual reproduction and is not applicable to fish reproduction methods.