Anemone that host tropical fish have been photographed spawning for the first time in the world by an Australian researcher.

Host anemone provide a safe haven for fish like Nemo the clownfish from the hit film Finding Nemo. But until now, researchers had never caught on film anemones' spectacular release of sperm and eggs.

Anna Scott, from the Southern Cross University in northern New South Wales, changed that by photographing anemone from the Solitary Islands Marine Park, 12 kilometres off the coast of Coffs Harbour.

Solitary Islands Marine Park contains the world's greatest density of host anemones, which are also found throughout the Indian and Pacific Oceans.

"We are confident that this is the first time that host anemone's spawning has been scientifically documented," Scott told ABC Science Online. "We're not sure why. It goes to show how much we have to learn about the fascinating marine world."

Scott photographed the event as part of her PhD after successfully predicting when the host anemones would begin spawning.

"[We assumed] they would spawn similarly to coral, according to a certain stimulus, such as the phase of the moon. We observed them from dusk until approximately 11 [at night] for 12 nights after each full moon."

Scott also took a series of samples from the anemones' gonads. By looking at how the eggs and sperm were developing, she calculated when they would be ready to spawn.

Host anemones are important as they provide an essential habitat for anemone fish, Scott said.

"Without anemones, the clownfish won't survive in the wild. [The anemones] also host a range of other creatures such as shrimp and crabs."

Anemone fish like clownfish are highly prized in the aquarium trade due to their fascinating relationship with their hosts, said Scott.

"Since virtually nothing is known about [anemone] sexual reproduction, collection relies on wild populations. This depletes local populations and potentially threatens their existence."

Researchers kept two species of host anemone Entacmaea quadricolor and Heteractis crispa in flow-through seawater tanks at the National Marine Science Centre in Coffs Harbour to keep conditions as close as possible to their natural environment.

Anemones have different sexes, and the males begin the spawning process, possibly cueing in the females, Scott said.

"Just prior to spawning and during the spawning process, the anemones became erect. The males ejaculate first, [their tentacles] go though an amazing series of contractions going up their column before an explosive release."

Scott said the males release sperm for 3 minutes, and go through this up to seven times in about an hour. The females then release a mass of fluid and tiny green eggs the size of poppy seeds, which float up through the water where the sperm fertilises them.

"The eggs and sperm float up and form a slick on the surface of the water, fertilisation occurs and they live there for some time then float back down and actively search about for a place to stay," Scott said.

The amount of fluid the anemone spawning produced was staggering, said Scott. Four anemones produced enough egg and sperm-filled fluid to completely cloud a 4000 litre tank.

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