PALAU » My two weeks of snorkeling in Palau are nearly over, and even though my husband, Craig, isn’t here, I can hear him ask the question he asks at the end of every adventure: What was your favorite part of the trip?

It’s always hard to choose one thing, but it’s particularly hard here with rock islands surrounded by coral reefs loaded with so many fish and invertebrates, my brain can’t take them all in. But when I close my eyes and recall my days here, one image pops out: the little fish in pajamas.

Palau hosts a reef species called the pajama cardinal fish, native to the western part of the tropical Pacific. The fish is so named because a black band around its middle looks like a waistband holding up red, polka-dotted pajama bottoms. A bright yellow top punctuated with big eyes and a body studded with permanently erect fins completes the image of a fish so adorable you want to give it a good-night kiss.

Pajama cardinal fish are nearly as tall as they are long, with adults growing to 3 inches. Even though small, the fish are easy to spot because five to 10 individuals often hover together outside branched corals. If you startle them, the fish dart into the safety of the coral’s arms, peeking out to see if the coast is clear.

But these cuties don’t startle as easily as other small fish. Usually, we found groups of pajama cardinal fish hanging like mobiles, the individuals motionless and facing the same direction.

“They look sleepy,” said one of my snorkeling companions.

“Of course they do,” my friend Lani said. “They’re in their pajamas and having a sleepover.”

The fish were inactive because the world’s 300 or so cardinal fish species rest during the day. At night they perk up to hunt tiny fish and crustaceans.

As if their appearance isn’t endearing enough, pajama cardinal fish have a remarkable method of reproducing.

The male guards the female as she lays her eggs. After fertilizing them, he scoops the whole load into his mouth. It’s then the female’s turn to stand guard and chase potential predators from her mate.

In three to four weeks, well-developed fry pop out of dad’s mouth. The male can’t eat while mouth brooding and can swallow up to 30 percent of the offspring. Oops.

As you might expect, pajama cardinal fish are favorites for home aquariums but they don’t have to be taken from the reef. Pajama cardinal fish are so mellow, they breed readily in tanks.

I like Craig’s question because it causes me to reflect on a trip’s highlights while they’re still vivid. Even so, I struggled in choosing pajama cardinal fish. Palau is all highlights.

Reach Susan Scott at susanscott.net.