Yes, it’s true. Sexual reproduction was invented by fish over 380 million years ago, long before dinosaurs roamed Earth. While we can’t see those ancient fish in action, modern descendants like sharks give us clues to the origin of sex: think rough-and-tumble encounters, siblings that eat each other in the womb, and the earliest examples of placentas, which beat mammals to the punch.
But sharks are just the beginning. Across the fish world, sex takes on a dazzling variety of forms. Some fish switch sexes once or multiple times throughout their lives. Others engage in chaotic mass spawning events, while a few opt for lifetime monogamy (with plenty of cheating on the side).
And when it comes to raising the kids? Strategies range from complete abandonment to devoted care, including mouth-brooding, embryo-carrying, and even outsourcing the job to another species.