British Beasts | Rocklings
Rocklings are elongated, slippery, scaleless fish; similar to lings, but smaller and rather more eel-like
They are gadoids, belonging to the same large family of fish as cod and ling. Other gadoid fish have chin barbels, but the snout barbels of rocklings are distinctive. Rocklings are relatively shy, and you are most likely to pick them out with a torch, hiding deep in a crevice. They also hide among seaweed, but on a night dive you may see them out hunting. They use a pair of elongated, feeler-like pelvic fins beneath the head to prop themselves up while resting on the sea bed.
However, the most curious feature of a rockling is its first dorsal fin, which moves constantly with a strange rippling motion. If you do get a chance to have a close look at a rockling, maybe in an aquarium, check out this fin, which is in a depression on the fish’s back just behind the head. At the front is a single spike (fin ray); just behind it the rest of the fin, which is a fringe of short rays that emerges from the groove running along the fish’s back. The rapid undulations of this fin, moving at around three to four beats per second, create a current of water across it. It has about 12,000 nerve fibres and is densely covered with between three million and six million sensory cells, which detect chemicals in the water, giving the fish a keen sense of taste. There are also taste buds on other fins and on the barbels, which feel the fish’s surroundings. The fish also has relatively large, sensitive eyes.
All these senses help the fish to identify and locate its food, which, when the fish is close enough, is rapidly sucked into its large mouth. Adult rocklings eat crabs, other small crustaceans, molluscs, small fish and occasionally polychaete worms and seaweeds.
Rocklings spawn offshore from winter to summer, depending on species and location. The eggs are buoyant and float in the surface waters. The tiny larvae stay near the surface for several months after hatching, often in dense shoals, and are known as ‘mackerel midge’ because they are a favourite meal for this fish. The tiny fish have camouflage: their green or blue backs and silvery sides and bellies make them difficult to spot from both above and below. Even so, a large proportion of the rocklings are eaten by other fish. The ones that escape sink to the sea bed at around 4–6cm long, change to a more appropriate brown colour, and take up a benthic life.
Little is known about the enemies of rocklings, but congers are reported to eat them, and larger fish in general are probably their main predators. Rocklings can occasionally be found at the fishmongers, as a bycatch from other fisheries.
Beast at a Glance
SHORE ROCKLING Gaidropsarus mediterraneus THREE-BEARDED ROCKLING Gaidropsarus vulgaris FIVE-BEARDED ROCKLING Ciliata mustela NORTHERN ROCKLING Ciliata septentrionalis
KNOWN HAUNTS The shore rockling usually lives in rocky areas, from the seashore to depths of about 30m. The other rocklings also inhabit sea beds of sand, gravel and mud. The five-bearded rockling lives mainly in shallow water to about 20m, while the three-bearded rockling can be found down to at least 150m. The northern rockling is scarcer and lives mainly in waters 10–100m deep.
BEST PLACE TO SEE The shore rockling is most abundant on the west coast of Britain, while the others occur all round Britain.
LIKELY TO APPEAR Present all year, but adult fish move offshore to spawn in winter through to summer, depending on species.
DISTINGUISHING FEATURES Stout, eel-like fish with two or four barbels on the snout and one under the chin. While the shore rockling has a very distinctive colouring of dark brown blotches on a pale background, the other three are uniform brown or slightly marbled with a paler belly. The three-bearded rockling has three barbels, while five-bearded and northern rocklings have five barbels, and are not easy to distinguish. The northern rockling is less common, and has a bigger mouth, extending well behind its eye.
SIZE The northern rockling is the smallest at only 15cm long. The five-bearded rockling grows to 25cm, the shore rockling to 35cm and the three-bearded rockling to more than 50cm.