Holding up the bag containing eight litres (14 pints) of the cloudy liquid, she says: "It looks like buko (coconut) juice, doesn't it."

The world's largest shell fish weighing up to 230 kilos (507 pounds) and measuring up to 1.4 metres (4.5 feet) in length, the Tridacna gigas was once a common sight in waters around the Philippine islands.

Highly prized for its meat and decorative shell the giant clam had virtually disappeared from the Philippines, fished out by local and foreign fishermen.

Shocked by the depletion of giant clam stocks marine biologist Edgardo Gomez decided to do something about it.

In 1985 when he was head of what is now the Marine Science Institute of the University of the Philippines he began an ambitious programme to breed and restock the bays and inlets around this southeast Asian archipelago nation of 7,000 islands.

"It really was a shock," he told AFP. "Giant clams are essential to coral reefs and so it was a race against time to build stock up."

Licuanan joined the programme around the same time, when she was a young marine biologist taking a four-year break in 1986 to complete her PhD on giant clams at Australia's James Cook University.

Married to a marine biologist who specialises in coral reefs and with three children she divides her time between her work and being a wife and mother.

On this particular Saturday she was collecting sperm and eggs from clams resting on the seabed off a small island in the Lingayen Gulf, six hours drive northwest of Manila.

Of the 10 known species of clams in the world the Philippines has seven and of that number Licuanan says it is the largest giant clam that is most at risk.

"Saving the giant clam has been a long process that has involved not only breeding and restocking but educating local fishermen that they are worth saving," she says.

"Clams form an integral part of a coral reef's ecosystem. At the same time they can also be farmed as a sustainable livelihood," she added.

Already reefs and bays in many parts of the Philippines are being restocked with mature giant clams from the project's protected ocean nursery areas off Bolinao in the Lingayen Gulf.

"Sometimes you feel like an expectant mother," Licuanan said, tapping a syringe containing serotonin.

"Serotonin is a neurotransmitter that induces the clam to adduct its valves to expel the sperm and eggs," she says. "Sometimes you have to give nature a hand in these things."

-- Giant clams are essential to the health of coral reefs --

Below the boat divers are busy selecting 20 adult clams ranging in age from seven to 10 years, number them and place them in a circle in less than two metres of water.

The thick shells are scrubbed with a nylon brush before the divers return to the boat to collect their syringes and begin to inject the clams.

Within 15 minutes the bivalves start to release clouds of sperm which is collected by the divers in plastic bags and delivered to the boat.

The bags are bought up and less than a litre of sperm is collected in a plastic container bearing each clam's number.

The rest, litres of it, is dumped back into the sea.

Giant clams spawn through an opening known as the excurrent siphon which looks like a miniature volcano on the underside of the clam.

As the clams start to spawn a plastic bag is placed over the outlet to collect the sperm.

Clams number 8 and 13 produce nothing. Then a diver appears calling out: "Eggs from number 8." Then another with: "Eggs from number 13."

"There is a scientific method of mixing sperm to eggs," Licuanan said as she poured the eggs into numbered plastic bags containing sperm.

"We tend to use too little of the sperm according to new data coming to hand."

Within two hours the collection is over and Licuanan is delighted with the day's efforts.

The best part for Licuanan is that the two clams that produced the eggs were young, only eight years old. She says this is close to the transition stage where clams produce both sperm and eggs.

"Clams are male when they are young, enter a transition stage when they are around eight producing eggs and sperm before crossing over and becoming female," she says.

Back at the laboratory peering down a microscope Licunanan estimates they had collected about 16 million fertilised eggs.

"If one percent make it past the hatchery stage you are doing pretty well," she says.

"The last clam spawning in May we managed to get 12 million fertilised eggs (and) from that we now have 200,000 clams in tanks in the hatchery measuring one centimetre in length.

"How many of them will survive the transfer to the ocean nursery where they will be put in cages suspended off the ocean bed we don't know. It's just up to nature."

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