For clownfish, it’s very much a man’s world because all clownfish are, in fact, born male. The most dominant male of the group will become female. There will only be one female per clownfish group. If she dies, then it’s normally down to the largest male to change sex and take her place.

Wrasses on the other hand work the other way, with groups being made of many females and one male. Exactly how this works is still something of a mystery, but it seems to consist of massive changes in hormone levels with ovaries transforming into testes. Amazingly, the fish can complete this transformation in as little as a week.

Things happen in nature, just like this.

Whilst this was once thought to be rare, sex changes have now been observed in several dozen fish families. For many, it seems to be a strategy to ensure that the individual can find a mate. For example in the deep sea, where densities are extremely low, it may be very rare to encounter another of your species—thus being able to change sex would be a huge advantage.