Christmas arrived early in 2018 for reef enthusiasts and marine fish keepers when it was announced that an unknown fish species had been discovered on northeastern Madagascar. This fish was discovered in relatively shallow waters in a reef near a city, and was mostly white in color — yet had never been seen before. Further, which genus this beautiful fish should be placed into confounded the experts, which added to the buzz of excitement surrounding it.

The species, which is new to science, was described and formally named Corazon’s damsel, Pomacentrus vatosoa, by ichthyologist Benjamin Frable, Collection Manager of Fishes at Scripps Institution of Oceanography, and Yi-Kai Tea, an expert on coral reef fishes and a PhD candidate at the University of Sydney studying systematic ichthyology, which is the science of classifying and naming new species, and understanding how they fit into the broader context of life.

Damselfishes are a diverse group of small- to medium-sized fishes that occur throughout the tropics and subtropics.

The newly-described damselfish has a striking pearlescent-white body color with two prominent black spots — one behind the pectoral fin near the middle of its body, and the second saddled across the upper edge of its tail where its fin connects to its body. It also has a sooty black stripe through its eyes that extends upward to its smokey grey dorsal fin that’s edged with electric royal blue. Although a common marking in butterflyfishes, this eye stripe is an extremely rare marking in damselfishes, according to Blue Ocean S.A.R.L., whose divers collected the fish (more here).

The fish’s conspicuous coloring and markings are what first caught the keen eyes of Brian Maravilla, a commercial diver working for the sustainable, ornamental fish export company based in Nosy Faho, a coral reef off the northeastern coast of Madagascar, in early December 2018.

The overall pattern of this mysterious fish’s markings somewhat resembled those of Stark’s damselfish, Chrysiptera starki, which lives on reefs in the far distant Coral Sea, suggesting it may be a new species of Chrysiptera. But because he’d never seen it before, Mr. Maravilla captured it and asked Mr. Tea to identify it.

“When I first received this fish, I was almost certain it was a new damselfish from the genus Chrysiptera,” Mr. Tea said in email. “This genus of damselfish is well known for harbouring some of the most beautiful species, and often they can be pearlescent such as with this one.”

Mr. Tea consulted with a number of fish experts around the world, and they all agreed that this was definitely something new, probably a new Chrysiptera species.

“I like teasing my fellow ‘fish nerds’ (as we call them) with photos of interesting fishes on my personal social media page, so I shared a photo of one just to get a vibe from the community. Often, great ideas get bounced around in such discussions,” Mr. Tea explained in email. “Everyone seemed to think it was a Chrysiptera, too.”

Having recently collaborated on another project with Dr. Frable, Mr. Tea and Dr. Frable again teamed up to work on identifying this mysterious fish. Mr. Tea used molecular techniques to investigate the fish’s genetic relationships and Dr. Frable examined the fish’s morphology — the detailed structure of its teeth, bones, scales, and its body shape.