The regal blue tang is a reef-dwelling surgeonfish with a hidden defensive weapon.

Nature · Published 3 October 2026 Swipe more like this →

In short: Known by many names, including the regal blue tang and hippo tang, this Indo-Pacific surgeonfish is a staple of marine aquaria. Beyond its striking royal blue body and yellow tail, it hides a sharp, retractable spine on its tail that can inflict deep, painful wounds when the fish feels threatened.

Paracanthurus hepatus is the sole member of its genus, characterized by a compressed, elliptical body and a distinct black palette-like design. These fish are diurnal residents of Indo-Pacific coral reefs, typically found at depths between 2 and 40 meters. They play a vital role in maintaining coral health by grazing on algae that might otherwise overgrow and choke the reef. Adults are omnivorous, feeding on zooplankton and various marine plants, while juveniles rely on plankton and seek shelter within Acropora corals.

The species is famous for its defensive caudal spine, located in a shallow groove on the caudal peduncle. When stressed, the fish extends these spines, which can cause significant injury to handlers. While the fish is not highly prized as food due to its strong odor and the risk of ciguatera poisoning, it is a major figure in the global aquarium trade. It is the 8th most traded marine ornamental fish worldwide, with nearly 95,000 individuals imported in 2011 alone. Unlike many other species, these fish are almost exclusively wild-caught, as captive breeding remains a difficult, nascent practice.

The regal blue tang gained massive pop-culture status following the 2016 film Finding Dory. While some feared a 'Nemo effect'—a surge in demand leading to over-collection—peer-reviewed analysis suggests that while online interest spiked, there was no significant corresponding increase in imports. Currently, the IUCN classifies the species as Least Concern, though it faces ongoing pressures from habitat destruction and overexploitation. With 80% of its family, the Acanthuridae, experiencing a 30% loss of coral reef habitat, conservationists emphasize the need for sustainable aquaculture to protect wild populations.

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