Common dragonet

Lore & Background

The common dragonet has a broad, triangular, flattened head with a long snout and protruding lower jaw; the body is also flattened, though the tail is rounded. Its eyes are placed on the top of the head, and the gills are also on the upper part of the body. The preopercular bone is strongly hooked and has four robust spines, the front facing forwards and the other three facing rearwards. Adults are sexually dimorphic: mature males have elongate rays in their dorsal and caudal fins, a yellowish second dorsal fin with bright blue longitudinal stripes, and bright blue marks on the head and body. Females and immature males are brown, paler on the underside, with a series of six brown blotches along their flanks and three symmetrical brown saddle-like blotches along the back with indistinct darker longitudinal stripes on the second dorsal fin. Their colour and patterning provide camouflage on coarse sand or gravel substrates, and when at rest on the seabed the fins are often folded.

The common dragonet is found in inshore waters from Iceland and Norway through the western coasts of Europe to Mauritania, as well as the Faroes, British Isles, Canary Islands, Madeira, Azores, the Mediterranean Sea, and the Black Sea. It occurs from the sublittoral zone to depths of up to 430 metres, most frequently between 5 and 50 metres, in temperate waters of 16–20 °C. It spends most of its time on the seabed partially buried in sand or shell gravel, with only the head and eyes protruding, and may emerge quickly to feed. It is an opportunistic feeder on small invertebrates such as worms and crustaceans; in one study crustaceans made up over 85% of the identifiable diet, with the porcelain crab Pisidia longicornis making up 43%. Molluscs, especially cockles, are also preyed upon. Common dragonets are an important prey item of Atlantic cod and pouting in the Irish Sea.

Male common dragonets are territorial and aggressively defend their territories from other males. Unlike many pelagic spawning fish, the common dragonet spawns as a pair, with an elaborate courtship: the male approaches the female, spreading his pectoral fins and erecting both dorsal fins to display his colours, while repeatedly raising his head and opening his mouth very wide. If the female responds, the male becomes more excited, and the pair swim vertically to the surface with the female resting on the male's pectoral fins, where eggs and milt are released between their bodies. After fertilisation, the eggs drift away in the current. Eggs, larvae, and postlarvae are pelagic, while juveniles prefer the intertidal zone.

Reader's Guide

The common dragonet is of minor importance to local commercial fisheries and can be found displayed in public aquariums. Its significance lies in its distinctive morphology and behaviour: the species exhibits strong sexual dimorphism, with males displaying bright blue markings and elongated fin rays, while females and immature males are cryptically coloured with brown blotches and saddle-like markings that provide camouflage on coarse sand or gravel. Its feeding ecology as an opportunistic predator of small invertebrates, particularly crustaceans like the porcelain crab Pisidia longicornis, and its role as prey for Atlantic cod and pouting in the Irish Sea, highlight its place in the food web. The elaborate paired spawning behaviour, involving vertical ascent and fin displays, contrasts with the more common pelagic spawning of many fish. The species is also notable for its wide distribution across the eastern North Atlantic, Mediterranean, and Black Sea, and its occurrence from shallow inshore waters to depths of 430 metres. Its use in the aquarium trade, though minor, contributes to its human relevance.

Did You Know?

• The common dragonet lives to a maximum age of around seven years.
• Males grow up to 30 centimetres (12 in) total length, while females average 20 centimetres (7.9 in).
• Its preopercular bone has four robust spines, with the front facing forwards and the other three facing rearwards.