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CRITTER: Moa the boxfish that was half male and half female

Over the past 15 years, it was my goal in Hawai‘i as a marine biologist to identify and shoot video of every fish species that occurs here, so I could do marine life identification movies for our school education program and also to educate tourists.

We now have a phone application where you can sit on the beach and pull up fish pictures and identify most of the species that live on our near shore shallow reefs. I supplied over 1,000 pictures to develop the application. The problem has been I keep finding fish I cannot identify.

Often after a dive shooting video, I will meet someone on the beach that saw a fish out snorkeling and they want to know what it was so I have them describe it to me.

We would look at the fish ID application, but we couldn’t find the fish they saw. We identify fish by their size, color, spots vs stripes or bands and also by fin shapes.

A few weeks back after snorkeling at ‘Anini Beach in Kaua‘i, one of the locals told me he saw a very strange colored boxfish out on the reef in about 3 foot deep of water.

The boxfish are usually super easy to identify because the males are bright blue with white dots on their back with a yellow face, and the females are solid black with white spots.

Boxfish are square shaped and about 6 inches long and they swim like an underwater helicopter. They can go forward, backward or even hover, and they are super fun to watch and quite common in shallow water lagoons.

I decided to go look for the odd colored boxfish the diver had described, and I ended up finding it and getting a close up video.

This boxfish did not look like a male or female and had the colors of both. The head was bright yellow with a blue chin, which would be a male’s color but the body was pure black with white dots which is the female’s color.

It turns out that the boxfish was in the process of converting from a female to a male and had both color patterns. We know that all boxfish are hatched out as females, but they have both female and male genetics.

Some of the females will change into males and completely change colors, but I have never seen this process take place until now.

It is almost impossible to identify a bunch of fish species that can completely change their sex and colors because when they are in the changing process they can look like a completely different species.

I would snorkel every few weeks to go visit this sex changing boxfish, and it took over three months for it to change from a female into a male.

The color change started around its mouth and ended at its tail. Other reef fish species that change sex can have their whole body change colors at the same time.

We have many fish species that are hatched out as females and change into males, so it is almost impossible to identify them during the few months it takes to change sex if you are looking at their colors. It is better to identify them by the shape of their body and fin structure.

The bottom line is there are a lot of fish out on the Hawaiian coral reefs that we just will not be able to identify except by DNA studies, so just have fun watching these amazing creatures change from girls to boys understanding that they have been doing this long before us humans arrived.

There are no “experts” when it comes to Hawaiian reef fish identification because so many of the fish go through a drastic color change and sometimes the fish go into deep water to convert from females to males, so we cannot observe these changes.

What will be fascinating to raise these fish in captivity, then we can monitor their sex changes and make it possible to identify them.

Captive breeding reef fish is getting more successful all the time, and 20 years from now we might be able to do a time lapsed video showing each species when they convert from female to male.

Feel free to monitor my marine life underwater educational webpage at, as we will announce our new free iPhone Hawaiian fish and reef creatures identification application soon.


Terry Lilley is a marine biologist living in Hanalei Kaua‘i and co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawaii go to
Source: The Garden Island

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