Diving in the waters of Samoa, Mark Erdmann watched as a haze of colorful little fish — each no bigger than a raisin — hovered over a coral reef, nearly motionless to avoid predators.

With the dazzling diversity of species that live on a coral reef, Erdmann, a Conservation International marine biologist, might have easily overlooked the dwarfgobies. To the untrained eye, they are nearly indistinguishable from dozens of similar species. But he glimpsed something new on the little fishes: a red stripe across the top of the heads and a pattern of white spokes radiating outward from the pupils.

He snapped a picture.

Photo by Mark Erdmann

Eviota taeiae.

“I immediately recognized it as a different species,” he said. “The satisfaction of recording another new species is the ultimate dopamine hit.”

It would take eight years to confirm Erdmann’s finding — delays in gathering data samples are not unusual when documenting a new species.…