Fivebeard Rockling

Fascinating facts about the Fivebeard Rockling

• A fish just 25 cm long can hide under a single tide-rock, thanks to its slender, scaleless body and a dorsal fin whose front part consists of a solitary ray followed by a line of vibrating rays without connecting membrane.
• From the Arctic waters of Finnmark down to Lisbon, this little predator lives across the eastern Atlantic, thriving in rocky intertidal zones and even in algae-covered breakwater pools.
• It never ventures deeper than about 20 m – the shallow limit where green algae can still grow – so its entire world fits inside a typical swimming-pool depth.
• Maturing at just one year old, a female can lay anywhere from 9,000 to 30,000 eggs, releasing them into the open ocean from February through May.
• Living in waters that swing between 8 °C and 24 °C, the species is of least concern but may be threatened by rising temperatures.

At a glance

About the Fivebeard Rockling

The fivebeard rockling (Ciliata mustela) is a sleek, elongated ray-finned fish that reaches up to 25 cm (9.8 in). Its body is smooth and scaleless, cloaked in a dark brown hue that fades to a pale gray-brown on the belly. Most striking are its five sensory barbels, two perched above each nostril and a single one on the lower jaw, plus a dorsal fin that begins with a solitary, free-standing ray before a line of vibrating rays runs in a furrow along the back, unconnected by membrane at the front. The rear dorsal fin and the anal fin extend the length of the body, their rays linked by a thin membrane, while the small mouth barely opens beyond the eye, hinting at a stealthy predatory style. In the intertidal zones of the eastern Atlantic, from Finnmark to Lisbon, including the Skagerrak, Kattegat, Iceland, and the coasts of Great Britain and Ireland, this rockling darts beneath rocks and in algae-laden breakwater pools, rarely venturing deeper than the 20-metre limit of green-algae growth. Its diet is a carnivorous medley of crustaceans, polychaetes, gastropods, and small fish, though occasional algae ingestion has been recorded. Remarkably, the species exhibits homing behaviour, returning to familiar shelters, and its reproductive cycle is swift: both sexes mature at about one year, with females laying between 9,000 and 30,000 eggs in February-May, releasing pelagic eggs that drift in the deeper Atlantic waters west of Ireland.

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