Ocean Watch

Last week, I received an e-mail from a friend about a fish she and her companion saw while snorkeling at Hanauma Bay. Amy wrote: "For the last two weekends, we have seen a small, very blue fish with a hint of yellow on his fins hiding close to the reef. His color is so bright and vibrant that it looks like nothing we have ever seen. Any ideas?"

No. But before I could look into it, Amy and her friend Brian found the fish's picture and name on the Internet. "It's a blue devil damselfish, Chrysiptera taupou," Amy wrote. "I read that it's one of the bluest fish in the ocean!" Nice work, I thought, except for one detail. Hawaii hosts 17 of the world's 320 kinds of damselfish, but the blue devil is not one of them.

Jeff Kuwabara, outreach coordinator for the Hanauma Bay Education Program, also knew about this fish, because a Bay volunteer spotted it and took pictures. Jeff sent the photos to Waikiki Aquarium biologist Norton Chan, who reports that this damselfish is indeed a Chrysiptera taupou, native to Samoa, Fiji and other parts of the South Pacific. How did a 3-inch damselfish get from there to here? No one knows.

It's not unusual to see damselfish in Hawaiian waters, and sometimes you don't have to get in the water to enjoy them. The Hawaiian sergeant, also called sergeant major, or mamo in Hawaiian, often swims in tide pools and shallow water. Like most other sergeant majors of the world, Hawaii's has a yellowish body with five black bars running down its side.

One endearing quality of sergeant majors is the male's bold defense of its fertilized eggs. The female lays a mass of purple eggs on a rock; the male fertilizes them and then defends them like mad.

And I mean mad. My first experience with a sergeant major happened in the Caribbean when I snorkeled up to one hovering near a purple splotch. Whack. The fish rammed my mask. That a 6-inch-long fish would attack a giant like me was so astonishing, I stayed to watch what would happen next. It nipped my arm.

Fortunately, no wrasses or butterfly fish went for the eggs while the little sergeant was busy fighting me off, but this is a danger when people get too close to damselfish nests. While the male is busy with the human, nearby fish can sneak by and eat the eggs.

The other Hawaii damselfish familiar to snorkelers and divers here is the Hawaiian dascyllus, also called the domino damselfish and one-spot damselfish. These pretty, black fish with a white spot on each side hover near branching coral heads and dart inside when predators approach.

Domino damselfish also duck into anemones for refuge like their famous South Pacific cousins, the clownfish.

But back to the blue devil (a hellish name for such a stunning beauty). How did a fish the size of a credit card swim from Samoa or Fiji to Hawaii?

Biologists here agree it probably didn't. Most likely, someone got tired of their aquarium and freed the fish in Hanauma Bay.

Releasing any alien species in Hawaii can cause incalculable harm and should never, ever be done. But since this little devil is here, we might as well enjoy it. Look for this nearly fluorescent blue fish among the rocks near the orange balls next to the channel leading outside the reef. And if you don't find time to get there soon, don't worry. Damselfish may live for 10 years.