Even if you don't know what Humphead Wrasse wrasse is, you'll probably immediately recognize it as a Napoleonfish. At Tokyo Sea Life Park 's "South China Sea" tank, you can see three Napoleonfish of various sizes.

This group of fish exhibits protogyny, meaning they first mature as females and then change sex to become males. This protogyny is commonly seen in fish of the wrasse family, to which the Napoleonfish belongs. In the case of the Napoleonfish, mature males have a protruding forehead, hence the name, which is reminiscent of the hat worn by the French emperor Napoleon.

The aquarium has always had three Napoleonfish of different sizes, but only the largest one was on display. This particular fish has a slightly protruding forehead, but it's impossible to tell from its appearance alone whether it's male or female. We wanted to display all three together in the same tank, but especially with the males, they can interfere with each other fiercely, and if a dominance hierarchy is established, the weaker one will always be bullied and chased around, so the other two were kept in a tank in the back area.

I came up with a plan to get the three of them to live together peacefully. It's difficult to add smaller fish to a tank that already has larger ones, so I decided to take out the largest one first, wait a few days, and then put the smaller ones into the tank in order of size.

About a month after introducing the smallest Napoleonfish, the second largest was introduced, and then another month later, on January 26, 2011, the largest one was introduced. At this time, the largest Napoleonfish had a slightly protruding forehead that was bright yellow, and it swam around trying to attract the attention of the two fish that were already there, threatening them and creating a tense situation, but so far there have been no fights or bullying.

Wrasse species spawn near dusk, and can be observed at aquariums just before the tank lights are turned off. There have been reports of Napoleonfish spawning being observed at some aquariums, so we hope to be able to observe it at Tokyo Sea Life Park as well.

[Tokyo Sea Life Park]

(February 4, 2011)