Blue-eyed Triplefin

Fascinating facts about the Blue-eyed Triplefin

• A blue-eyed triplefin can be as tiny as a fingernail, measuring just 3 cm, yet some individuals grow to 6 cm – about the length of a standard paperclip. Its size lets it slip into the tiniest cracks of reef rock where larger fish can't follow.
• When you count its stripes, you’ll find exactly nine vivid red bars that run straight down its body, like a barcode for the sea. Those bars, paired with an orange-tinged head, make it easy to spot among the gray stones of New Zealand’s North Island reefs.
• In winter, male blue-eyed triplefins turn their orange heads, tails, and anal fins into a brighter flame while the rest of their bodies darken to blue-black. This dramatic color flip signals readiness to guard a nest and warns rivals away.
• Males carve tiny depressions into vertical rock faces at depths of 10–20 m and coax females to lay their eggs there. Once the clutch is deposited, the father stands guard, turning the rock face into a protected nursery.
• A 2017 survey recorded just 58 individuals of this species, underscoring how a fish that can clean parasites off larger companions is still a rare jewel of New Zealand’s coastal waters.

At a glance

About the Blue-eyed Triplefin

The blue-eyed triplefin (Notoclinops segmentatus) is a small reef dweller, measuring 3 to 6 cm in length. It has iridescent blue eyes, nine red vertical bars around the body, and an orange tinge on the head and back. In the winter breeding season males show brighter orange on the head, tail, and anal fin, while the rest of the body becomes blue-black. These fish live on broken-rock reefs around New Zealand’s North Island at depths of about 1 to 30 m, and males build nests in small depressions on vertical rock faces at 10–20 m depth, which they guard after females lay eggs. Their diet includes small crustaceans such as amphipods and copepods, and they have been observed removing parasites from larger fish. The 2017 fish count recorded 58 individuals.

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