The Kobudai: Meet The Gender Changing Fish

The adage about truth being stranger than fiction is never more evident than in nature. Our earth abounds with extraordinary creatures that have developed the abilities to do extraordinary things in their quest for survival in what are often adverse conditions. And, while technology and innovative methods of research are enabling us to learn more and more about the animals and other organisms with which we share the planet, there is undoubtedly so much more we have yet to discover.

The Kobudai: A Gender Changing Fish

Some of our most fascinating wildlife lives in the world's oceans, and in his latest documentary series, Blue Planet 2, naturalist Sir David Attenborough introduces a host of astonishing marine creatures, many that had never before been captured on film. One of these is the striking-looking Kobudai fish, found in the oceans around Japan, which has the impressive ability to change genders. As Sir David Attenborough puts it in his inimitable style: 'Inside every female Kobudai there is a new male in waiting.'

Semicossyphus reticulatus, which is also sometimes known as the Asian Sheepshead Wrasse, is not the only hermaphroditic fish in the sea, sharing the characteristic (in some form) with around 500 other species. Some, like the Kobudai, go from female to male, some from male to female, and others are able to switch back and forth at will.

While it is not entirely clear why some female Kobudai switch gender and others don't, scientists concur that the reason behind the change itself is a reproductive strategy. Males are able to pass on more genes, therefore providing an evolutionary advantage.

Making the Change

Once they reach a certain age females are able to undertake the gender transformation, and researchers in Japan have observed that water temperature is a major factor in the timing. At an optimal temperature of 16 degrees Celcius the mating season begins and, at the same temperature, females begin to turn into males – with the window of opportunity only lasting about two or three weeks. If there is an abundance of dominant males it's less likely a female will make the change, but if there are weaker males in the group, the chances are far greater.

One the change begins, the female hormones are effectively switched off and the fish begins to produce male hormones.They develop an aggressive nature, testes and the male's distinctive bulbous forehead, with the process taking anywhere from a few weeks to several months.

Capturing the Images

Because of the extended period of time it takes for the fish to complete its gender change, it was not practical for the Blue Planet 2 team to follow an individual to observe the change from start to finish. Instead, using rebreathers to reduce the disturbance to the fish (an apparatus that produces fewer bubbles and is much quieter than regular SCUBA equipment), the team filmed multiple individuals over two seasons in order to capture the incredible footage.

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Our oceans are truly the last great wilderness areas on the planet and professionally organised wildlife cruises are often the only way to access places unable to be reached by air or land. The opportunity to encounter fascinating marine and terrestrial wildlife in its natural habitat makes wildlife cruises among the most privileged and sought after nature travel experiences.

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Marissa Ellis-Snow is a freelance nature writer with a special interest in marine species. For nature lovers interested in dedicated wildlife cruises, Marissa recommends thetours organised by Naturetrek, which have brought her unforgettable sightings of a wide range of species in one of the most spectacular regions on Earth.