We’re not clownin’ around! Clownfish are all born as males and become females later in life. So in “Finding Dory”, Nemo’s dad would have become Nemo’s mom—and by the next sequel, Nemo might be his own sister!
Many fishes change sex as they grow. Called sequential hermaphroditism, this strategy helps maximize the number of offspring individuals can have over their lives. Clownfish are protandrous—meaning “male first"—while the California sheephead is protogynous, beginning life as a female and growing into a "terminal phase” male. Depending on your perspective, that’s either a tragedy or an improvement!