By Matt Walker
Editor, Earth News
A mirror of each other
One of the most elegant courtship rituals in the animal kingdom has been captured on film by a BBC crew.
The dance of the weedy sea dragon takes place every year in the shallow seas off the coast of Australia.
During the ghostly dance, two beautifully odd-looking fish mirror each other's every movement.
At the end of the ritual, the male fish is the one to get pregnant, giving birth two months later, a process the BBC crew filmed for the first time.
The dance of the weedy sea dragon is captured for the BBC natural history series
Weedy sea dragons are a type of fish related to seahorses and pipefish.
Two species exist. The
weedy sea dragon
(Phyllopteryx taeniolatus) lives among weed beds in the seas off the southern coast of mainland Australia and Tasmania.
leafy sea dragon
(Phycodurus eques) lives further along the southern and western Australian coast.
When a male and female weedy sea dragon come together to mate, they perform an elaborate courtship ritual known as a "mirror dance".
Looking for a partner
"It's an amazingly engaging sequence, because it is so beautiful and graceful, and yet totally observed," says Adam Chapman, a BBC producer who helped film the behaviour with cameraman Doug Anderson.
"There is no sense that they are at all concerned about anything other than each other."
The mirror dance usually takes place in the fading evening light.
In a graceful duet, each partner mirrors the actions of the other, swimming and wriggling their bodies.
"What's so lovely is you feel you have seen the most intimate moments of their lives," says Mr Chapman.
The ritual usually takes place in spring.
With the help of independent biologist and leading sea dragon expert Mr Pang Quong, the BBC filmed the sequence in October, around two miles southeast of Melbourne.
After two months, the results of the courtship are revealed.
A baby sea dragon is born
Sea dragons, seahorses and pipefish are the only fish species in which the males carry and raise the young.
In doing so, the male weedy sea dragon keeps them safe until the eggs are ready to hatch.
After two and half weeks of diving, Mr Anderson caught the act of a male sea dragon giving birth on camera.
The "dance of the sea dragon" is broadcast within the Fish episode of the BBC series
at 2100BST on BBC One on Monday 2 November.