Three dragonet species visit British seas, but the common dragonet is much larger and more widespread than the other two (the reticulated and the spotted). The dragonets form a fairly large family of fish, most of them living in the warmer seas of the world. They are particularly abundant in shallow parts of the western Pacific.
Colour and flash
Long and slender, the common dragonet’s head and belly are flattened on the underside. The mouth is fairly large and is situated rather on the underside of the head. The frog-like eyes are placed high on the head, and the fish has a long curved snout.
The pectoral fins are broad, like the pelvics which spread out laterally. The long-based dorsal fins are high, and the males in particular have extremely long rays in the first dorsal fin.
The male has spectacular colouring -warm brown on the back with blue spots, and head and fins striped with pale blue and yellow. Females are more modest -brownish with three brown ‘saddles’ across the back and brown spots on the sides.
A mud burrower
With its semi-flattened body, the dragonet is well suited for life on the bottom – especially on sand, mud or a mixture of the two. It is most common at depths between 20m and 100m (65-440ft), but can be found down to 120m (385ft). Small numbers of immature fish can be caught in much shallower water- 3.5m (lVAft) or so.
It burrows into the upper few inches of the sea bed and lies with its eyes and top of the head and back above the surface. It gets oxygen by pumping water over circular gill openings at the top of the gill covers just behind the eyes.
No detailed studies of the dragonet’s diet have been made, but scattered observations suggest they eat small crustaceans, worms and various molluscs. It seems that it is a unselective feeder, eating the most common bottom-living organisms available.
The dragonet spawns in early spring, usually during February and March. The male and female have an elaborate courtship which takes place on or close to the bottom before they spawn. The male displays his brightly coloured dorsal fins and head close to the female (in a large male these fins are strikingly high as well as brilliant blue and yellow). After this display both fish surge upwards off the bottom for up to 50cm (20in), simultaneously discharging the eggs and milt. The fertilized eggs float to the surface. In early summer the planktonic young may be extremely abundant.
The female dragonet may live up to seven years, while the male lives only for five. The male grows faster — though he doesn’t become sexually mature until he’s three or four years old. A study of the biology of the dragonet some years ago indicated that the male spawned only once before dying, but this still needs to be confirmed.