The family Callionymidae includes 9 genera and about 130 species, many living in tropical seas, often unobserved due to their small size and their cryptic habits. They are bottom fish, mostly living in shallow water on sandy or muddy sediments where they can bury themselves.
Dragonets have naked, scaleless skin covered with a slimy mucus layer, which gives off a strong odour in many species, hence the name stinkfish. The head is large and spiny, with prominant eyes. The body is elongated, with large fins, the dorsal fin is dividend into 2 parts, the first part is greatly elongated in males. It is colourful when extended, and used to attract females. The small mouth can extend in a downward tube which helps in catching its prey of worms, shellfish and small crustacea from within the sediment.
Bottom dwelling dragonets tend to be sandy-coloured and well camouflaged. They glide along the bottom and seem to disappear by keeping still and/or quickly burying themselves. However, during territorial disputes and mating rituals the Festive-robe dragonet, Callionymus pusillus, a Costa Brava species, reveals why it is so named, spreading its fins to display glimmering colours.
Males guard the largest possible territory to better their chances of encountering a nomadic female. Since there is no way to differentiate their boundaries, territorial disputes are frequent and involve a curious tornament. The dragonets charge at each other, stopping just short of contact and standing rigid with upraised heads, gaping jaws, and outspread fins. If neither backs down they fight by locking jaws, pushing and shaking until the victor is determined and the loser retreats.
When the male encounters a female, he performs a brilliant display to impress her. The interested female responds by repeatedly hoisting and lowering her dorsal fin. The male then grasps the female with his pectoral fins and the pair swim very slowly upward. About a meter off the bottom, the female releases her spawn, which is immediately fertized by the male. The pelagic eggs are left to drift in the plankton. The pair separate quickly and retreat to the sandy bottom.