Bluestripe Fangblenny

The Bluestripe Fangblenny (Plagiotremus rhinorhynchus) is a combtooth blenny in the family Blenniidae, widespread across coral reefs of the Indo-Pacific from the Red Sea to the western Pacific. It is well known for its close visual resemblance to the Bluestreak Cleaner Wrasse, a mimicry it uses to approach other reef fish under the guise of offering a cleaning service before darting in to nip scales, mucus, fins, or occasionally small bites of flesh with enlarged fangs on its lower jaw. This form of aggressive mimicry is a notable example of Batesian-style deception in reef fish ecology. The species is common and not considered threatened, and is frequently studied as a case example of mimicry and antagonistic fish interactions on Indo-Pacific reefs.

• Body: elongated, slender, blenny-shaped, typically 10-12 cm
• Marking: a bold dark blue-black stripe running the length of the body against a pale blue to white background
• Head: pointed snout with visible enlarged fangs at the front of the lower jaw
• Fins: single long, low dorsal fin running most of the body length

The Bluestripe Fangblenny is frequently confused with the Bluestreak Cleaner Wrasse (Labroides dimidiatus) due to near-identical coloration, but can be distinguished by its more elongated, blenny-like body shape, less fluid swimming style, and visible fangs, versus the wrasse's more streamlined body and smooth undulating swim.

This species is found on coral reefs throughout the Indo-Pacific, from the Red Sea and East Africa to Southeast Asia, Australia, and the western Pacific. It typically occupies reef slopes and flats at depths of 3-40 meters, favoring areas with plentiful coral cover and a diversity of other reef fish that serve as targets for its mimicry-based feeding strategy. It is most often seen hovering near coral heads, ready to dart out toward passing fish, and shelters in coral crevices or abandoned worm holes when not active.

The Bluestripe Fangblenny relies on aggressive mimicry, closely imitating the appearance and some movement patterns of the cleaner wrasse to approach other reef fish that expect a beneficial cleaning interaction. Instead of removing parasites, it uses enlarged fangs to nip a scale, patch of mucus, or small piece of fin or flesh before quickly retreating to cover. Individuals are largely solitary and hold loose territories around a home coral head. The species is a protogynous hermaphrodite capable of changing sex, and spawning involves brief pair formation near shelter sites. Its venom-associated fang glands are used defensively against predators rather than in its feeding strikes on other fish, and it plays a distinctive ecological role as a deceptive micro-predator among a reef's otherwise cooperative cleaning interactions.