Sex-Swapping Swimmers

Beneath the ocean waves lies a mysterious world filled with strange animals. Some of the most recognizable are the many species of clownfish. More than a funny face, these flashy fish have the amazing ability to change sex from male to female. To Christians, this might sound morally fishy. After all, humans were created in the image of God as either male or female, though our culture increasingly attempts to rebel against that good design. But the Creator has intentionally given these fish sex-swapping superpowers to maintain healthy populations.

Clowning Around

An animal’s ability to express both male and female characteristics is called hermaphroditism. Simultaneous (or synchronous) hermaphrodites have fully functional male and female reproductive organs and are sometimes capable of self-fertilization. In contrast, sequential (or successive) hermaphrodites start life as one sex but can change into the opposite sex—like clownfish.

Clownfish are all born male and live in groups called schools. Leading each school is its largest member, a dominant female, who chooses the strongest male to become her partner. Once the dominant female dies, her mate transforms into a female, who will then choose a new male to be her reproductive partner.

But clownfish are not the only fish designed as hermaphrodites—nearly 500 species (2%) of fish exhibit this extraordinary ability.

Just Keep Swapping

In contrast to clownfish, which are all born male, Asian sheepshead wrasses (also called kobudai) are all born female. If an imbalance occurs in the ratio of males to females in a habitat, large females may transition into males. Over several months, females will hide away to transform. Their chins and foreheads will swell into prominent bulges, and their bodies will double in size. They emerge from hiding fully male and ready to reproduce.

A third sex-swapper is the dwarf hawkfish. Like the kobudai, dwarf hawkfish start their lives as females. They live in harems, where one dominant male protects and reproduces with many females. If a harem grows too big for him, the largest female transforms into a male and takes some of the females to form a new harem.

Unlike clownfish and kobudai which permanently swap sexes, the dwarf hawkfish doesn’t have to stay a “he” for long. If he is challenged by a larger male, he can switch back to “she” and become a member of the more dominant male’s harem.

One of the most remarkable hermaphroditic fish is the chalk bass, which can switch sexes up to 20 times per day. While the previous fish were sequential hermaphrodites, chalk bass are simultaneous hermaphrodites. Despite all chalk bass possessing male and female reproductive organs, they don’t self-fertilize. Instead, males and females partner up and switch parental roles throughout spawning.

Designed to Deviate

Unlike humans whose sex is determined by chromosomes, the sex of many fish is influenced by other factors such as water temperature.

One reason fish can swap sexes so easily is that, unlike humans whose sex is determined by chromosomes, the sex of many fish is influenced by other factors such as water temperature, water acidity, chemical pollutants, or even parasites. An enzyme called aromatase often controls whether fish become male or female, since their gonads have the potential to develop into ovarian or testicular tissue. When fish are triggered to swap sexes by environmental factors, aromatase is often at play.

However, in other fish, like many mentioned above, sex-swapping is triggered by social circumstances. God likely designed hermaphroditism in these fish to guarantee greater reproductive success. In clownfish, only the strongest individuals become females, ensuring the best genetics are passed along to future generations. Kobudai and dwarf hawkfish switch sexes to maintain the balance of males and females in a population. Chalk bass switch parental roles to ensure proper energy distribution during spawning.

Made in God’s Image

At first glance, hermaphroditic fish seem as though they could be mascots for a world that increasingly accepts gender fluidity. Steeped in an evolutionary worldview, our culture often looks to nature for moral guidance or approval, since they believe humans are also animals. Because certain animals can switch sexes, some people claim this is proof that it’s natural for humans to decide to change genders. But basing human morality on animal behavior is bound to result in terrible consequences. After all, animals often engage in what humans categorize as cannibalism, murder, rape, theft, and torture.

God makes it clear that humans are not animals. Animals are subject to their genetics and instincts because they lack a God-given sense of morality. Conversely, humans are moral beings uniquely made in the Creator’s image (Genesis 1:26–27). Because we can choose to do right or wrong, God gave us laws to follow. Unfortunately, Adam and Eve chose to disobey God, and all of creation and its creatures are now cursed by sin (Genesis 3).

The world tries to separate sex and gender, making concessions for mixing and matching according to their perceived identity.1 But nowhere does Scripture distinguish between sex and gender. God made humans either male or female (Genesis 1:27), and we are incapable of changing into the opposite sex at a biological level. Though extremely rare, human hermaphrodites do exist, but not by choice. Their condition is the result of an abnormality in their DNA or a change in development, both ultimately caused by the effects of the fall.

Fish swap sex not because of personal choices of identity but because of mechanisms God placed within them to transform at a biological level to survive in ever-changing ecosystems. These sex-swapping swimmers join a multitude of other animals with magnificent designs that point to an infinitely ingenious Creator.