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A small team of ichthyologists at the California Academy of Sciences has discovered a new species of damselfish living off the shores of the Maldives. In their paper in the journal ZooKeys, the group describes how they found multiple examples of the fish while on an expedition that involved exploring deep-sea coral reefs off the coast of the Maldives—an island chain in the Indian Ocean, southwest of India—and features of the newly discovered fish.

The new species was discovered as the team used hand nets to capture, identify and release fish living on and around the deep-sea corals. In contrast to shallow coral reefs, the researchers point out that deep-sea reefs are poorly studied, particularly those in the Indian Ocean, the eastern Atlantic and the eastern Pacific. Thus, it was no great surprise for them to find a species of fish that had not been classified before. The team named it Chromis abadhah as a nod to the funders of the project.

The research team describes the newly found species as having a pale, ghostly blue underside with a white top. They noted the blue color changed shades along its length. Also, those they observed in nets from eight sites around the Maldives averaged 6.9 cm in length—and were netted below 100 meters.

At that depth, they pointed out that not much light gets through—it is part of the mesophotic zone. The two-tone coloring of the fish, they further noted, was common for deep sea fish, as it helps them from being seen from both above and below.

C. abadhah, they found, lived in or near crevasses, close to populations of sea sponges—a clear sign that the fish is popular among predators. The researchers note that fish living in the mesophotic zone tend to have a lot of commonalities, with certain species filling the niche roles. They do not know yet which niche C. abadhah is filling.

The team concludes by noting that deep sea reefs do not face the same risk from rising acidity due to increasing amounts of carbon dioxide in the air as shallow reefs do, but still face other human-made hazards such as nets and ropes that fall from ships, bleaching and trash—all of which likely also present a danger to the fish that live there as well.

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